Tens of thousands of anti- and pro-government demonstrators have gathered in Tehran as tensions deepened after Ahmadinejad was declared the runaway winner of presidential polls on Friday.

Obama also said he believed that Ayatollah Ali Khamenei, Iran's supreme leader, understood that there were deep concerns in Iran about the disputed poll, as the biggest opposition protests since the 1979 Islamic revolution escalated.

Twitter request

In depth



 Video: Iranians go online to evade curbs
 Video: The struggle for power
 Video: Rival protests continue in Iran
 Video: One dead at Iran rally
 Video: Iranians rally in Europe
 Video: Poll result triggers Tehran protests

 
Iran curbs media after poll result
 Mousavi sees election hopes dashed
 Iran writer on poll result
 Mousavi's letter to the people
 Iran poll result 'harms US hopes'
 West concerned by Iran fraud claims
 What next for Iran?
 The Iranian political system
 Inside Story: Iran's political future 

Despite Obama's vow not to meddle in Iran's internal affairs, the US government said it had asked mobile social networking site Twitter to delay scheduled maintenance.

The site has been used as a communication tool by protesters, especially since the Iranian government shut down many websites, cell phones and newspapers.

Twitter delayed Monday's scheduled maintenance, which would have taken place during daylight hours in Iran, and rescheduled it for Tuesday.

"They announced they were going to shut down their system for maintenance and we asked them not to," a US state department official said on condition of anonymity.

The firm however, told Al Jazeera that US government pressure had not contributed significantly to its decision to delay the temporary shutdown.

"The decision to alter the maintenance schedule wasn't affected by any one voice. Twitter simply understood that the reliability of the platform has become critical in people's lives across the globe," it said.