Iran sank into deeper isolation from the West on Wednesday, with Britain pulling out all of its diplomats and U.S. officials pushing for the European Union to take a tough line against Tehran during a crucial meeting planned for Thursday.

The moves come after a well-organized attack by Iranian hard-liners Tuesday on two British diplomatic compounds in Tehran, including the embassy. The attack, which appeared to have official approval, set off a series of retaliatory moves in which Britain on Wednesday ordered the closure of its heavily damaged embassy within 48 hours.

Germany, one of Iran’s largest trading partners, recalled its ambassador “for consultations,” as did France, Italy and the Netherlands.

But the main decision on how to respond to the events in Tehran will come Thursday in Brussels, when foreign ministers from the 27-member European Union will hold a scheduled meeting on Iran.

There, options range from reducing embassy staff to withdrawing ambassadors and closing all of the member states’ embassies in the country.

“We are clearly going to see a much tougher stance by the Europeans toward Iran following this event,” said one Tehran-based Western diplomat, who spoke on the condition of anonymity. “After the Brits were ransacked, the E.U. has no other choice but to stand up against Iran.”

Western diplomats and politicians said that any severing of relations would be a perilous choice for both the European Union and Iran at a time when tensions over Tehran’s nuclear program are high.

But U.S. officials pointed to the potential upside of what they said was a strategic error by Iran to authorize the storming of the British sites.

“There is a strong view that Iran massively overreached,” said an Obama administration official, who spoke on the condition of anonymity to discuss the White House’s internal reaction to the events. “Iran has given the international community a condemnable act to rally around.”

Despite the damage to the British sites, some U.S. and European officials consider the exodus of diplomats as an encouraging sign. More than ever, they said, Iran is finding itself with few allies and friends — particularly in the developed world but also among countries traditionally friendly with Iran. Statements by Russia and China denouncing the embassy attack were viewed on Wednesday with particular satisfaction.

“You’re seeing both a chorus of international condemnation as well as actions on the part of countries around the world that I think reflect Iran’s isolation,” State Department spokesman Mark Toner told reporters.

The immediate diplomatic response remained unclear, however. While legislation that would significantly tighten sanctions on Iran continued to work its way through Congress, the White House was not expected to announce new economic penalties beyond measures adopted in November. But U.S. officials were hopeful that European allies would vote to further sanction Iran at the E.U. meetings on Thursday. The measures under discussion include new curbs on Iran’s petroleum industry.

“Anyone who might have been squishy on sanctions before now has reasons to act,” the Obama administration official said.

As a group, European nations are the third-largest buyers of Iranian oil and have traditionally acted as intermediaries when the Islamic Republic has tried to reach out to the United States, with which it has no diplomatic relations.

Catherine Ashton, the E.U. foreign policy chief, has worked to facilitate talks between the world’s major powers and Iran on the Iranian nuclear program.

Toner, asked whether a military response appeared more likely after the Tuesday assault, repeated the administration’s standard formulation, saying: “We’ve always said all options remain on the table.” But he added that the White House remains committed to its “two-track” approach of increasing economic and political pressure while seeking to engage Iran’s leaders or — if they’re unwilling — ordinary Iranians.

“The door remains open,” he said.

Western diplomats, meanwhile, continued to ponder Iran’s reasons for allowing such a blatant — and internationally prohibited — violation of Britain’s diplomatic sanctuary.

Some Iran experts considered the attack evidence of Iranian frustration after a series of setbacks this year — including additional sanctions, a weakening of its key strategic allies in Syria, and a number of recent explosions and disasters involving nuclear and missile facilities and experts.

“There would be some among the Revolutionary Guard who are convinced that Britain — as well as the U.S. and Israel — have had a hand in recent assassinations of nuclear scientists, sabotage of nuclear installations and explosions in military bases,” said Ervand Abrahamian, an Iranian-born professor at City University of New York and author of a history of modern Iran. “Since the U.S. and Israel do not have embassies in Iran, the British become the obvious targets.”

One diplomat visited the British Embassy grounds Wednesday to search for the British ambassador’s dog, which was found. The diplomat said damage to the buildings was extreme.

“The place had been systematically ransacked, paintings were destroyed and furniture was broken,” the diplomat said. “We have concluded that the attack had been extremely well coordinated by the authorities.”

Security forces initially allowed groups of young men armed with sticks to pillage the diplomatic compounds Tuesday and to briefly detain six embassy staff members.

Members of the volunteer Basij militia smashed windows, set fires and hurled satellite dishes from a roof on the embassy compound while police looked on. The demonstrators, who numbered about 300, were denouncing Britain’s decision to impose harsh sanctions on Iran in response to new revelations about the Islamic Republic’s efforts to acquire technology that could be used to build nuclear weapons. The attack brought back memories of the 1979 seizure of the U.S. Embassy in Tehran.

While Iranian President Mahmoud Ahmadinejad has remained silent about Tuesday’s rampage, he “does not want this crisis,” said a Western diplomat based in Tehran.

But Tuesday’s events could play into the hands of Ahmadinejad’s domestic rivals. The attackers were lauded Wednesday by several supporters of the hard-line clerics and Revolutionary Guard commanders who oppose the president.

Ali Larijani, Iran’s speaker of parliament and former top nuclear negotiator, said the demonstrators represented Iranians’ true feelings toward Britain.

“It is the British government’s behavior which is shameful because they have behaved in a hostile manner toward our people for the past five decades,” he said.

Warrick reported from Washington. Correspondents Anthony Faiola in London and Michael Birnbaum in Berlin and staff writer Karen DeYoung in Washington contributed to this report.