President Trump stiffened his posture anew toward Iran on Monday after Tehran showed no sign of releasing a British oil tanker that its forces seized in the Persian Gulf and claimed to have arrested 17 CIA spies.
“It’s getting harder for me to want to make a deal with Iran,” said Mr. Trump, who called the claim of spy arrests a “totally false story.” His remarks showed a shift in tack after weeks of attempts by the White House to publicly open the door to negotiations with Tehran.
“They put out propaganda, they put out lies,” said Mr. Trump, underscoring frustration toward Iran’s government that appeared to be mounting within his administration and in Europe.
In Britain, outgoing Prime Minister Theresa May convened an emergency meeting of her Cabinet to discuss strategies toward freeing the Stena Impero, a British-flagged oil tanker that Iran’s military captured Friday in the Strait of Hormuz. Tehran has refused to release the ship and its 23 crew members.
Britain, which has been reluctant to join Mr. Trump’s campaign of pressure and economic sanctions against Iran and has tried with other European powers to salvage an Obama-era Iranian nuclear deal, took a harder line Monday.
“The ship was seized under false and illegal pretenses, and the Iranians should release it and its crew immediately,” May spokesman James Slack told reporters. “We do not seek confrontation with Iran, but it is unacceptable and highly escalatory to seize a ship going about legitimate business through internationally recognized shipping lanes.”
Britain also announced plans to form a “maritime protection mission” in which European nations will use escort vessels to help ensure the security of commercial ships traveling anywhere near Iran.
The ramped-up rhetoric suggested that Iran’s strategy of provocation — multiple ship detentions, bombings of several oil tankers, the downing this month of an American drone and pledges to ramp up nuclear enrichment activities — may be driving London and Washington away from the prospect of diplomacy with Tehran.
Even as Iran faced widespread international condemnation for its takeover of the Stena Impero, officials in Tehran took another dramatic step by claiming to have captured 17 U.S. spies. Some of them, Iranian officials said, have been sentenced to death.
“The rulings for these spies have been issued, and a number of them will be executed as corruptors on earth,” said an Iranian official whom the semi-official Fars News Agency identified only as a counterespionage chief.
The official said Washington had offered U.S. visas in exchange for those arrested — all Iranian citizens — to act as spies inside their country.
Secretary of State Mike Pompeo, a former CIA director, flatly dismissed the claims.
“The Iranian regime has a long history of lying,” said Mr. Pompeo. “I think everyone should take with a grain of salt everything that the Islamic Republic of Iran asserts today.”
Meanwhile, Iranian officials have rejected demands from the British government to release the Stena Impero and its crew, although Tehran did release video Monday showing the crew appearing healthy.
In justifying its actions, Iran said Britain struck first this month by detaining a ship that was carrying Iranian oil destined for Syria. The ship was captured near Gibraltar, and Britain has maintained that the vessel was rightfully held because oil shipments to Syria violate international sanctions.
Iran’s government has a different view.
“When you illegally seize a ship in Gibraltar … we don’t deem it as necessary to show tolerance,” said Ali Rabiei, an Iranian government spokesman. “Some countries have asked for the immediate release of the British tanker. Well, we ask those countries to make the same request to Britain first.”
Iran has wreaked havoc in the Strait of Hormuz in recent months in direct response to Trump administration pressure to uphold a global embargo on purchases of Iranian oil. The administration has threatened U.S. economic sanctions on any foreign companies that buy or transport the crude.
U.S. officials this weekend announced Operation Sentinel, a plan to increase security and surveillance in the region. The plan centers on persuading nations to provide military escorts to non-Iranian commercial oil vessels traveling through the Strait of Hormuz and elsewhere in the Persian Gulf.
Dozens of nations around the world rely on oil transported through the Gulf from Saudi Arabia, the United Arab Emirates, Kuwait and Iraq.
White House National Security Adviser John R. Bolton was in Tokyo on Monday and was expected to push for Japanese officials to contribute to the increased security and surveillance effort in the region.
It was not immediately clear whether Mr. Bolton had secured an agreement from Japan, which has significantly cut its purchases of Iranian crude oil in recent months in line with Washington’s embargo.
“I’m sure those discussions will continue over the next days and weeks. I’m very optimistic about the outcome,” said Mr. Bolton, according to The Japan Times.
The U.S. also has pushed its allies in Europe to join an economic pressure campaign against Tehran. After Mr. Trump withdrew from the multinational 2015 nuclear deal, Washington imposed economic sanctions against Iran. The administration says the approach is working despite Tehran’s continued provocations.
“Their Economy is dead, and will get much worse,” Mr. Trump tweeted Monday. “Iran is a total mess!”
Administration officials have said the increased sanctions are designed to pressure Iran into negotiations that address issues beyond suspect Iranian nuclear activities — particularly Tehran’s ballistic missile program and backing of proxy militias across the Middle East.
Britain and other leading European nations have refused to embrace the U.S.-led sanctions campaign and have stuck by terms of the 2015 nuclear agreement, which lifted sanctions on Iran in exchange for limits on Tehran’s nuclear program.
But Mrs. May’s government has indicated in recent days that Britain may pursue its own sanctions against Iran if Tehran does not release the Stena Impero and its crew.
⦁ Tom Howell contributed to this article, which is based in part on wire service reports.