TEHRAN (Reuters) - An Iranian official accused the United States on Friday of involvement in a mosque bombing that killed more than 20 people in volatile southeastern Iran, two weeks before a presidential election.

Washington denied the allegation.

Jalal Sayyah, of the governor’s office in Sistan-Baluchestan province, said three people had been arrested in connection with the blast on Thursday in a crowded Shi’ite mosque in the city of Zahedan, in a region where many of Iran’s minority Sunnis live.

“The terrorists, who were equipped by America in one of our neighboring countries, carried out this criminal act in their efforts to create religious conflict and fear and to influence the presidential election,” Sayyah told state radio.

A Sunni opposition group named Jundollah (God’s Soldiers), which mainly Shi’ite Muslim Iran says is part of the Islamist al Qaeda network and backed by the United States, said it was behind the bombing, Saudi-owned Al Arabiya television said.

The Dubai-based station said a man called it saying it was a suicide attack aimed at Basij forces, a religious militia, meeting in the mosque to coordinate election strategy.

It was not possible to verify the claim of involvement of Jundollah, which says it fights for the rights of Iran’s Sunnis.

Supreme Leader Ayatollah Ali Khamenei also suggested Iran’s foreign enemies were involved in the blast, saying “no one can doubt that the hands of...some interfering powers and their spying services are bloodied by the blood of the innocent.”

The U.S. State Department denied involvement in the bombing.

“We condemn this terrorist attack in the strongest possible terms,” State Department spokesman Ian Kelly said. “We do not sponsor any form of terrorism in Iran.

Sayyah said two children were among the dead. The official IRNA news agency put the death toll at 25 and named most of the victims, all males. Other media gave somewhat lower figures.

The person who detonated the device was standing among men praying in Ali Ebne-Abitaleb mosque and was also killed, provincial judiciary official Ebrahim Hamidi said.

Iranian media said a big part of the mosque was destroyed by the blast. Footage showed a blood-stained floor inside.

Slideshow ( 5 images )

It was one of the deadliest such bombing incidents in Iran since its 1980-88 war with Iraq. A blast in a mosque in the southern city of Shiraz killed 14 people in April last year but the country has been relatively peaceful in a turbulent region.

“It has been confirmed that those behind the terrorist act in Zahedan were hired by America and the arrogance’s other hands,” Sayyah told the semi-official Fars News Agency.

Iranian leaders, who often accuse the United States and its allies of seeking to destabilize it, refer to Washington as the “Great Satan,” guilty of “global arrogance.”

Slideshow ( 5 images )

Iran has also previously accused its arch-foe of supporting Sunni rebels operating on its border with Pakistan.

U.S. INVOLVEMENT DOUBTED

Sistan-Baluchestan province, home to Iran’s mostly Sunni ethnic Baluchis, is the scene of frequent clashes between security forces and heavily armed drug smugglers and bandits.

Defense analyst Paul Beaver said it was “highly unlikely” that the U.S. administration of President Barack Obama, who is seeking to engage Tehran diplomatically after three decades of mutual mistrust, would support Sunni insurgents in Iran.

He said history had shown that backing guerrilla groups to effect regime change was “ineffectual and wrong, and the present U.S. administration does not want to be tarnished in that way.”

In an incident on Friday in the same city, three people were wounded when gunmen on a motorbike opened fire on the local campaign headquarters of President Mahmoud Ahmadinejad in Zahedan, IRNA said.

Police later arrested the attackers, it said. Two of the wounded worked in the election office. A child was also hurt.

In April, Iran’s intelligence minister said it had arrested a group of people linked to Israel who were planning bombings before the June 12 election, in which the conservative incumbent, Ahmadinejad, is seeking a second four-year term.