A bomb exploded in southeastern Iran late Friday, near the site where an earlier explosion this week killed 11 members of Iran's elite Revolutionary Guards, the state-run news agency IRNA reported.
"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.
The semiofficial Fars news agency said clashes broke out between Iranian police and armed insurgents following the explosion in Zahedan but those reports could not be immediately confirmed.
On Wednesday, a car bomb blew up a bus owned by the elite troops in Zahedan, capital of the Sistan-Baluchestan province on the border with Pakistan.
Friday's blast came just hours after the funeral of the 11 Revolutionary Guardsmen took place in the provincial capital.
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 come amid growing tensions between Tehran and Washington over insurgency in Iraq and Iran's controversial nuclear activities.
The Fars agency said the Friday explosion occurred at a female school in Zahedan.
"The insurgents began shooting at people after the explosion. Clashes are continuing between police and the armed insurgents. Police have cordoned off the area," the Fars agency said.
Iran's state-run television showed footage of Zahedan residents marching in the streets earlier in the day and 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 on the People's Mujahedeen opposition television, run by the armed group, minutes before Friday's explosion. 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.