MOSCOW, June 15 (RIA Novosti) - Iranian President Mahmoud Ahmadinejad has put off a trip to Russia for a regional summit starting on Monday, the first foreign visit after his disputed reelection, an official at Iran's embassy in Moscow said.

"The president has delayed the visit to Russia," the official told RIA Novosti by phone, adding that the visit might take place on Tuesday or Wednesday. He did not give further details.

Tehran and other Iranian cities were swept by mass protests at the weekend over alleged vote fraud in the landslide reelection of the hardline president.

Ahmadinejad was due to attend the two-day summit of the Shanghai Cooperation Organization (SCO), bringing together Russia, China and four ex-Soviet Central Asian republics, in the Urals city of Yekaterinburg. The Islamic Republic, like India, Pakistan and Mongolia, holds observer status in the group, which traditionally focused on security but is increasingly encompassing economic and energy projects.

Ahmadinejad was due to meet with President Dmitry Medvedev on the sidelines of the summit on Monday to discuss bilateral ties and Iran's controversial nuclear program.

Russia is completing the construction of Iran's first nuclear power plant and has supplied nuclear fuel for it. The international community suspects Iran of seeking to build a nuclear bomb under the guise of the civilian program, something that Tehran denies.

Thousands of supporters for Ahmadinejad's reformist challenger Mir Hossein Mousavi gathered on the streets of Tehran on Saturday, protesting against alleged ballot fraud. The demonstrations turned violent, with rioters burning police motorcycles and smashing shop windows. Police fought back the protesters with batons and tear gas. According to protesters, several dozen people were arrested.

Smaller-scale riots continued on Sunday, but were reported to have been postponed on Monday after the Interior Ministry declared they would be illegal.