Foreign powers urged citizens to avoid travel to Iran on Monday as Tehran focused its anger on London and European leaders closed ranks against accusations of meddling.
Britain, Italy and Germany all warned its nationals against non-essential travel to Iran, with London also pulling out family members of embassy staff after radical students threatened its premises in Tehran.
France warned its tourists still in the country against taking pictures and said rallies should be avoided.
Iranian lawmakers urged a review of ties with Britain as radicals labelled its government "perverted" and warned that Tuesday could be another "November 4," the date when Islamist students captured the US embassy in Tehran after the 1979 revolution.
Iran's wrath and accusations of "meddling" in the post-election protests led the European Union to declare Tehran's charges "baseless and unacceptable."
The Czech EU presidency summoned the Iranian charge d'affaires in Prague and "categorically rejected Iran's claim that positions expressed by the EU and its member states constitute illegitimate interference in Iran's internal affairs".
Italian Foreign Minister Franco Frattini later said that a US-backed invitation for Iran to attend the G8 foreign ministers meeting it is hosting later this week was no longer practical.
"I have to consider that Iran has declined the invitation," he said.
Heightened diplomatic tensions came after riot police armed with clubs fired tear gas on Monday at about 1,000 opposition protesters who defied an official ban on demonstrations.
The clashes followed a violent crackdown on protesters in Tehran Saturday that claimed 10 lives, bringing the toll over the past week to at least 17.
"Further violence is possible," the British Foreign Office said when issuing its travel warning.
Germany said it "invited" Iran's ambassador to clarify the charges of interference, a foreign ministry spokesman said.
The day before, Chancellor Angela Merkel had called for a recount in the June 12 election that returned hardline President Mahmoud Ahmadinejad to power, triggering mass opposition protests and charges of vote fraud.
Swedish Foreign Minister Carl Bildt, whose country assumes the rotating EU presidency on July 1, said the right to stage peaceful protests was protected in the Iranian constitution.
"Certainly the use of lethal violence against peaceful demonstrators is never tolerated in any country," he said.
The White House said that no "justice" had been achieved in Iran, following President Barack Obama's warning to Tehran to avoid "violent and unjust" actions towards its people.
"You have seen violence ratchet up appreciably," said spokesman Robert Gibbs.
Democrats say the president has rightly taken a hands-off approach, with officials insisting there are no US "fingerprints" on the unrest.
Among allies, Russia's foreign ministry called for a constitutional resolution to the crisis, while emphasising "good neighbourly relations" with Tehran.
And neighbouring Syria turned its criticism on the protesters.
"Anyone betting on the fall of the Iranian regime will be a loser," said Syrian Foreign Minister Walid Muallen.
The post-election protests are the biggest popular upheaval in Iran since the 1979 Islamic revolution.
Foreign media have been restricted in reporting on the crisis but images of police brutality have spread worldwide via amateur video over the Internet.
Canadian Prime Minister Stephen Harper called on Iran to halt its assault on press freedoms and release all political prisoners and journalists.