Leaders from around the world expressed concern over the situation in Iran, given new reports of government-inspired violence against election protesters and alleged voter fraud.
The US ratcheted up its response after defeated Iranian candidate Mirhossein Mousavi called for an investigation into the Friday's Presidential election, demanding the results to be annulled.
The European Union followed suit Monday, increasing pressure on Iran to agree to opposition demands to investigate President Mahmoud Ahmadinejad's landslide election victory and halt a crackdown on protesters.
The presidency is concerned about alleged irregularities during the election process and post-election violence that broke out immediately after the release of the official election results on 13 June 2009, the office of the EU Presidency said.
Republican Senator John McCain called the reelection of Ahmadinejad corrupt and urged the United States to speak out strongly in the same way the EU was.
The Obama administration expressed concern but officials are also reiterating weekend comments by Vice President Joe Biden that the administration still aims to try direct diplomacy to cease its pursuit of a nuclear weapons capability and stop supporting terrorism.
US State Department spokesman Ian Kelly told the press Monday morning that the United States is closely watching the events unfolding in Iran and deeply troubled by reports of violence arrests and possible voting irregularities.
The enthusiasm and robust debate these elections engendered captured the attention of the world. And the essential right of people to express themselves peacefully needs to be respected, he noted.
The international community remains committed to seeing Iran living up to its international responsibilities, and we will continue to use all avenues to try to convince Iran to meet its international obligations, he said.
Iran's Guardian Council said it would rule within 10 days on two official complaints it had received from Mousavi and another losing candidate, Mohsen Rezaie. It's chairman Ayatollah Ahmad Jannati endorsed Ahmadinejad before the vote.
The council vets election candidates and must formally approve results for the outcome to stand.
The German government believes the allegations of manipulation of the vote must be examined quickly by the responsible bodies to remove the doubts about this result, government spokesman Thomas Steg told reporters in Berlin.
Ahmadinejad and Interior Ministry officials have dismissed allegations the vote was rigged. The president has called the election free and healthy.
The Tehran government has banned international observers from the balloting, limiting options the International community has.