The United States last night cast doubt over the re-election of Iranian President Mahmoud Ahmadinejad, while France said the situation set back hopes of better relations between Tehran and the international community.
When asked if he believed Mr Ahmadinejad had won the vote, which the opposition say was rigged, US Vice President Joe Biden said: "We have to accept that for the time being but there's an awful lot of question about how this election was run.
"It sure looks like the way they're suppressing speech, the way they're suppressing crowds, the way in which people are being treated, that there's some real doubt," he told NBC's Meet The Press, adding "We don't have enough facts to make a firm judgment."
US President Barack Obama has urged the Iranian leadership to "unclench its fist", but hopes of improved ties between Washington and Tehran may be complicated by the events at the weekend. The US will want to continue (as yet unsuccessful) efforts to engage Iran in nuclear diplomacy, but cannot appear to condone any internal suppression of dissent.
With Mr Ahmadinejad claiming to have won almost 64 per cent of the vote, he is likely to feel more emboldened and defiant. He was whipping up the crowds yesterday with bellicose rhetoric. "America and other countries, you threaten Iran and you'll get your answer!" he bellowed.
David Miliband, the Foreign Secretary, said the allegations of vote rigging were a matter for the Iranian authorities to address. "We will continue to follow developments," he said in a statement. "Our priority is that Iran engages with the concerns of the world community, above all on the issue of nuclear proliferation."
Iran has proceeded apace with its uranium enrichment programme, which it says is geared towards generating electricity but which the West suspects is aimed at making bombs.
France, a permanent member of the UN Security Council and part of the group of six world powers trying to persuade Tehran to halt its nuclear ambitions, described the current situation as extremely worrying.
"What is happening in Iran is clearly not good news for anyone, neither for the Iranians nor for peace and stability in the world," said Henri Guaino, one of President Nicolas Sarkozy's closest advisors.
French Foreign Minister Bernard Kouchner, who met with George Mitchell, President Obama's Middle East envoy, in Paris yesterday, added: "France regrets that instead of openness there has been quite a brutal response ... This will leave its mark, and the opposition will organise itself ... Brutality and never-ending military development will not bring any solutions."
As the major Western powers wrestled with how to respond to Mr Ahmadinejad's declared victory, official congratulations poured in from Afghanistan and Pakistan, both neighbours of Iran as well as US allies. And Hassan Nasrallah, the Hizbollah leader, sent the Iranian president a personal letter. "Your re-election represents a great hope to all the oppressed people, holy worriers and resistance fighters who reject the powers of arrogance and occupation," he said.