WASHINGTON — Tensions between the United States and Iran flared on Monday as Tehran said that it was likely to breach a key element of the 2015 international pact limiting its nuclear program while President Trump ordered another 1,000 troops to the Middle East and vowed again that Iran would not be allowed to develop a nuclear weapon.
The Pentagon’s announcement of the troop deployment came three days after attacks on two oil tankers in the Gulf of Oman that the administration has blamed on Iran. And it came hours after Iran said it was within days of violating a central element of the landmark 2015 agreement — intended to curb its ability to develop a nuclear weapon — unless European nations agreed to help it the impact of tough American economic sanctions.
Iran’s Atomic Energy Organization said that within 10 days the country will have produced and kept in its stockpiles more low-enriched uranium — the sort used to fuel power plants — than allowed by the 2015 containment deal, from which the Trump administration withdrew last year. The agency also left open the possibility that it might soon begin enriching the uranium to higher levels of purity, edging it closer to what would be necessary to build a nuclear weapon.
The White House responded with a call for greater international pressure on Iran. “President Trump has made it clear he will never allow Iran to develop nuclear weapons,” the National Security Council said in a statement.
The developments add to escalating tensions between Washington and Tehran that have called into question the effectiveness of President Trump’s pressure campaign, and European officials urged restraint between the two longtime adversaries.
The additional 1,000 troops being sent to the region come on top of 1,500 dispatched in May. They will be used primarily for additional surveillance of Iranian activities and further protecting American forces already in the Middle East.
“The recent Iranian attacks validate the reliable, credible intelligence we have received on hostile behavior by Iranian forces and their proxy groups that threaten United States personnel and interests across the region,” the acting defense secretary, Patrick Shanahan, said in a statement.
The announcement from Tehran was Iran’s latest signal that it will abandon the 2015 pact unless other signatories help Iran circumvent economic sanctions imposed by Mr. Trump. The threat seemed aimed primarily at European countries, to persuade them to break with Washington and swiftly restore some of the economic benefits of the deal to Tehran.
Iran had been abiding by the terms of the nuclear deal, negotiated under President Barack Obama, before Mr. Trump pulled out, and has continued to do so since the withdrawal by the United States. But as American sanctions have squeezed the Iranian economy, Tehran has warned that it could not remain in the deal without getting European help to find workarounds to the sanctions.
“This was an entirely predictable consequence of the Trump administration’s withdrawal from the nuclear deal and maximum pressure strategy,” said Ali Vaez, director of the Iran project at the International Crisis Group, a conflict-resolution organization. “In practice, maximum pressure has produced maximum peril and minimum strategic results.”
[The U.S. has turned up the pressure on Iran. See the timeline of events.]
The mechanism of American sanctions may actually have sped Iran to the point where its stockpile of uranium is on the verge of violating the 2015 agreement’s terms. In May, the State Department announced that it might penalize countries that transfer enriched uranium out of Iran. Until now, Iran has shipped most of the low-enriched uranium it produces out of the country, swapping it for natural uranium. That allows it to continue producing small amounts of nuclear fuel for civilian power plants without building up a stockpile for potential use in a weapons program.
During a news conference announcing Tehran’s decision, Behrouz Kamalvandi, a spokesman for Iran’s Atomic Energy Organization, said Iran might also enrich its uranium up to 20 percent purity for use in reactors, the Iranian state-run news organization Press TV reported.
He said that uranium would be used as fuel for the Tehran Research Reactor, which the United States supplied to Iran in 1967 and that Iranian officials say is used to create medical isotopes for use in cancer treatment.
The nuclear agreement limits the level of enrichment to 3.67 percent, but if Iran began producing 20 percent enriched uranium, it would put the country much closer to weapons-grade levels.
Tensions between the United States and Iran have steadily increased since Mr. Trump withdrew the United States in May 2018 from the nuclear agreement, one of many signature Obama administration policies that Mr. Trump had pledged to cancel during his presidential campaign.
Over the last year, the Trump administration imposed severe economic sanctions that have discouraged most outside companies from doing business with Iran, and followed that up with measures to cut off Iran’s oil revenues, the lifeblood of its economy. The sanctions have had a great impact on Iran, including leading to a shortage of critical medicine within the country, despite Secretary of State Mike Pompeo’s assertions that humanitarian aid would not be affected.
In April, Mr. Trump designated the Islamic Revolutionary Guards Corps, an arm of the Iranian military, as a foreign terrorist organization, despite warnings from Pentagon and C.I.A. officials that the move could lead to reprisals against Americans. As tensions rose, Mr. Trump said he was adding 1,500 troops to the Middle East.
Recent attacks on oil tankers in the Strait of Hormuz, which the Trump administration has blamed on Iran, have further inflamed matters.
The Pentagon released additional pictures on Monday that it said bolstered its case that Iran was responsible for the attack on the tankers last week. Tehran has denied responsibility.
Defense Department officials said one of the images shows sailors with Iran’s Islamic Revolutionary Guard Corps removing an unexploded limpet mine from one of the tankers, the Kokuka Courageous, in the hours after an initial explosion. Another photo, the Pentagon said, shows the “remnants of the magnetic attachment devise of unexploded limpet mine” placed on one of the tankers.
The officials said the limpet mines were placed above the water line of the ships, where they would be visible but would do relatively limited damage, and not below the water line, where they could actually cause the ships to take on water. One official, speaking on ground of anonymity, said that the Pentagon interpreted this as Iran trying to send a message of what its capabilities are in the Gulf, without doing real damage to shipping.
The official described it as a “nuisance attack” and said the Pentagon viewed it as calculated.
A National Security Council spokesman, Garrett Marquis, said Monday that Iran’s announcement on its nuclear program was “nuclear blackmail” that “must be met with increased international pressure.” The White House national security adviser, John R. Bolton, has been a longtime advocate for regime change in Iran.
On Sunday, Mr. Pompeo said that the United States might further tighten sanctions on Iran in response to any moves to ramp up its nuclear program.
“We know that their nuclear program accelerates if they have more money and wealth, if they have more capacity, more resources, they have access to metals and to materials and to fissile material,” he said on “Face the Nation” on CBS.
Mr. Pompeo also said that the United States was considering “a full range of options” in responding to the attacks on tankers in the Strait of Hormuz, including military strikes. Pressed on whether he thought an existing congressional authorization for war would cover hostilities with Iran, Mr. Pompeo avoided answering, as he did in April during a hearing on Capitol Hill.
The United States has considered getting international support to create a naval force that would provide security for oil shipments in the region, similar to the antipiracy coalition assembled in the Arabian Sea in recent years.
“China gets over 80 percent of its crude oil transiting through the Strait of Hormuz,” Mr. Pompeo said. “South Korea, Japan, these nations are incredibly dependent on these resources. We’re prepared to do our part.”
China was an important contributor to the antipiracy venture, but may not be willing to join a United States-led effort to protect shipping. China and Russia were both signatories to the 2015 nuclear agreement and have opposed Mr. Trump’s Iran policies. Beijing has said it intends to continue buying oil from Iran despite American sanctions.
Over the weekend, Mr. Pompeo spoke with a member of the Chinese Communist Party’s Politburo and a half-dozen foreign ministers, a State Department spokeswoman said Monday.
On the nuclear agreement, Mr. Kamalvandi, the spokesman for the Atomic Energy Organization, said
Iran would stay within the uranium enrichment limits if Britain, France, Germany and the full European Union — all of which are signatories to the nuclear deal — followed through on plans to give Iran access to international financial systems, sidestepping American sanctions, and made up for lost oil revenue.
“As long as they comply by their commitments, these will go back,” Mr. Kamalvandi said at news conference at the country’s Arak nuclear plant.
Germany, Britain and France have worked to set up a system to allow European companies to take part in a kind of barter trade with Iran.
The mechanism, called Instex, is still in its early stages and relies on Iran to set up a similar system internally. But, at best, it is only a way to trade in goods not formally covered by the sanctions, including medical goods, food and humanitarian supplies.
In early May, President Hassan Rouhani of Iran set a 60-day deadline for the Europeans, who hope to salvage the deal, to make good on promises to help preserve Iran’s oil and banking sectors.
But Mr. Rouhani was careful to stress that while Iran would retain its enriched uranium and heavy water rather than selling them to other nations, it would stay for now within the limits set by the nuclear deal.
Monday’s announcement was the first time Iran’s government had said explicitly that it would step beyond the pact.
On Sunday, Helga Schmid, a senior Europe Union diplomat, visited Tehran for meetings on the nuclear deal. Ms. Schmid, who helped negotiate the 2015 agreement, reiterated her support for the deal and discussed options to enable trade between the bloc and Iran, Reuters reported.
If Iran does break the limits of the deal, the Europeans will have to consider bringing the case to the United Nations Security Council and perhaps reimpose their own economic sanctions.
The Netherlands’ foreign minister, Stef Blok, said Monday that European support for the nuclear deal depended on Iran adhering to the pact’s terms.
“It’s very important to keep on verifying through the international atomic agency whether Iran is still fulfilling the criteria,” he said. “As long as Iran is fulfilling these criteria, we should stick to this deal.”
Mr. Blok was attending a meeting of European Union foreign ministers in Luxembourg. The ministers called for further investigation of responsibility into the attacks on two tankers in the Gulf of Oman last week. The Trump administration released a grainy black-and-white video that it said showed an Iranian patrol boat pulling up to one of the damaged tankers and pulling an unexploded limpet mine off the hull. European officials say the video evidence is not conclusive.