Iranian riot police and militiamen appear to have halted protests in the capital, Tehran, after days of clashes over the country's disputed election, reported BBC.
Residents say the city is quiet, but opposition supporters have called for a day of mourning on Thursday for those killed during the protests.
One defeated presidential candidate, Mosen Rezaie, a conservative, has now withdrawn his complaint.
Barack Obama has condemned the "unjust" violence used against protesters.
Meanwhile, reports say four Iranian footballers who appeared to show solidarity with them have been banned.
The pro-government Iran Daily newspaper said four of the six players who wore green wristbands during a World Cup qualifier against South Korea in Seoul had been retired from the national team.
The US president's comments on the situation in Iran came as the UK expelled two Iranian diplomats in response to the expulsion of two of its own officials from Tehran.
The Iranian authorities have accused Britain and the US of trying to destabilise the country, something they have denied.
In the 12 days since the 12 June election, which saw incumbent President Mahmoud Ahmadinejad returned with 63% of the vote, opposition supporters have repeatedly clashed with police on the streets of Tehran.
On Tuesday, President Obama used his starkest language yet to strongly condemn Iran's clamping down on election protests.
He said he respected Iran's sovereignty and it was "patently false" of Iran to say the West was fomenting the unrest.
Mr Obama said: "The United States and the international community have been appalled and outraged by the threats, beatings, and imprisonments of the last few days.
"I strongly condemn these unjust actions and I join with the American people in mourning each and every innocent life that is lost."
He said: "The United States respects the sovereignty of the Islamic Republic of Iran, and is not at all interfering in Iran's affairs. But we must also bear witness to the courage and dignity of the Iranian people, and to a remarkable opening within Iranian society."
Earlier on Tuesday, the opposition was told by Iran's Guardian Council, the legislative body for elections, that the presidential election result would not be annulled.
Iranian hardline students burnt the US and British flags outside the British embassy in Tehran
Flags were burnt outside the British embassy in Iran
Guardian Council spokesman Abbas Ali Kadkhoda'i said there had been "no major fraud or breach in the election".
But Iran's Supreme Leader Ayatollah Ali Khamenei later agreed to extend by five days the amount of time allowed to examine complaints of electoral fraud.
Mohsen Rezaie, who is a former leader of the Revolutionary Guards, said he had withdrawn his complaints about the vote in the interests of Iran's national security.
"I see it as my responsibility to encourage myself and others to control the current situation," Mr Rezaie was quoted as saying in a letter to the Guardian Council.
He had previously claimed to have won more votes than the official tally which placed him third place in the poll.
The remaining two candidates have called for the elections to be re-run, amid claims of vote tampering.
Opposition candidate Mehdi Karoubi has urged Iranians to mourn for dead protesters on Thursday.
His call echoed an earlier one from cleric Grand Ayatollah Hossein Ali Montazeri for three days of national mourning for those killed in the street protests.
The UK moved to expel two Iranian diplomats in response to Tehran's decision to order two UK diplomats to leave Iran following allegations UK Prime Minister Gordon Brown called "absolutely without foundation".
Mr Brown told the BBC: "We want a very good relationship with the Iranians, we also respect the fact that it's for the Iranian people themselves to choose who their government is.
"But when there is a sign of repression or where there is violence that's affecting ordinary people in the streets, we have a duty to speak out and to say we want Iran to be part of the world, we don't want Iran to be isolated from the world."
The Iranian parliament's national security and foreign policy commission responded to the expulsion of the diplomats in London by reconsidering ties with Britain.
The meeting was attended by Foreign Minister Manuchehr Mottaki and the Iranian state broadcaster said certain decisions were made in the meeting that would be announced in due time.
On Friday, Ayatollah Ali Khamenei banned protests, prompting street violence in which at least 10 people died.
Severe reporting restrictions placed on the BBC and other foreign media in Iran mean protest reports cannot be verified independently as correspondents are unable to move around the city freely or cover unauthorised gatherings.
Are you in Iran? What do you think of the current situation? Are you taking part in the demonstrations?