"Minutes ago, the sound of a bomb explosion was heard in one of Zahedan streets," the agency said but gave no further details. IRNA didn't say whether the explosion had caused any deaths or injuries.

But the semiofficial Fars news agency quoted the governor of Zahedan, Hasan Ali Nouri, as saying the blast was a "sound bomb explosion"-a device that creates a loud boom but that usually does not cause casualties.

Nouri said there was gunfire heard but that it was late at night and that police had cordoned off the area.

Fars had said that after the blast, which took place near a female school, clashes broke out between Iranian police and armed insurgents in Zahedan, capital of the Sistan-Baluchestan province on the border with Pakistan.

The reports could not be immediately confirmed.

The Friday blast came just hours after the funeral of the 11 Revolutionary Guardsmen killed here Wednesday when a car bomb blew up a bus owned by the elite troops in Zahedan.

A Sunni Muslim militant group called Jundallah, or God's Brigade, which has been blamed for past attacks on Iranian troops, has claimed responsibility for the Wednesday bombing.

Iran has accused the United States of backing militants to destabilize the country. The accusation comes amid growing tensions between Tehran and Washington over insurgency in Iraq and Iran's controversial nuclear activities.

Iran's state-run television showed footage of Zahedan residents marching in the streets earlier Friday, carrying coffins of the killed Guardsmen for burial. The crowd chanted, "death to hypocrites," in a reference to the insurgents.

Separately, IRNA quoted an unnamed "responsible official" late Friday as saying that one of those arrested on charges of involvement in Wednesday's bombing, identified as Nasrollah Shanbe Zehi, has "confessed" that the attacks were part of alleged U.S. plans to provoke ethnic and religious violence in Iran.

"This person who was behind the bombing confessed that those who trained them spoke in English," IRNA quoted the official as saying. According to the official, the suspect was surprised at his arrest, because he had allegedly been told that the people would support the group.

The confessions by Zehi helped police detain an unspecified number of Jundallah members and confiscate weapons and documents from the group in a raid Thursday in Zahedan, IRNA also said.

A majority of Iran's population are Shiite Muslims but minority Sunnis live in southeastern Iran.

The blasts represent sharp flare-up of violence in the remote southeast corner of Iran, near Pakistan and Afghanistan, that has long been plagued by lawlessness. The area is a key crossing point for opium from Afghanistan and often sees clashes between police and drug gangs.

Jundallah, believed to have links with al-Qaida terror group, has waged a low-level insurgency in the area, led by Abdulmalak Rigi, a member of Iran's ethnic Baluchi minority, a community that is Sunni Muslim and is present in Pakistan and Afghanistan. Rigi has said his group is fighting for the rights of impoverished Sunnis under Iran's Shiite government.

The Fars agency also said that said Rigi appeared the opposition television belonging to the Iraqi-based People's Mujahedeen, minutes before Friday's blast. The group seeks to overthrow the Iranian government by force.

Iranian officials have often raised concerns that Washington could incite members of Iran's many ethnic and religious minorities against the Shiite-led government in Tehran.

Iran has faced several ethnic and religious insurgencies that have carried out sporadic, sometimes deadly attacks in recent years - though none have amounted to a serious threat to the government.

In December, Jundallah claimed responsibility for kidnapping seven Iranian soldiers in the Zahedan region, threatening to kill them unless group members were freed from Iranian prisons. The seven were released a month later, apparently after negotiations through tribal mediators.

In March 2006, gunmen dressed as security forces killed 21 people on a highway outside Zahedan in an attack authorities blamed on "rebels," though Jundallah was never specifically named.

The Canadian Press, 2007