Iran hanged 13 members of a Sunni Muslim rebel group Tuesday convicted of bombings and killings in the country's restive southeast near the borders with Pakistan and Afghanistan, the state news agency reported.

The mass execution was the largest ever carried out against members of Jundallah and was likely meant as a warning to the group, which is composed of Sunnis from the Baluchi ethnic minority. They have waged a low-level insurgency in recent years, accusing the mostly Shiite and Persian Iranian government of persecution.

The group, whose name means Soldiers of God in Farsi, took credit for a homicide bombing of a Shiite mosque in May that killed 25 people in Zahedan, the capital of Iran's southeast Sistan-Baluchistan province that has witnessed some of Jundallah's worst attacks.

The 13 men were scheduled to be hanged in public in Zahedan, but authorities changed their minds at the last minute and decided to execute them inside the city's main prison, according to the official IRNA news agency. The report said Abdulhamid Rigi, the brother of Jundallah's leader, Abdulmalik Rigi, had been scheduled to be hanged, but his execution was postponed. It gave no reason for the postponement.

The executions were the latest by Iranian authorities seeking to quell violence in Sistan-Baluchistan province. Three men convicted of having links to the homicide bombing in May were hanged only two days after the attack.

But the government has struggled to enforce order in a region where the problem of sectarian violence is combined with the challenge of cracking down on drug smuggling routes connected to neighboring Pakistan and Afghanistan.

Jundallah has carried out bombings, kidnappings and other attacks against Iranian soldiers and other forces in recent years, including a car bombing in February 2007 that killed 11 members of Iran's elite Revolutionary Guards near Zahedan.

Jundallah also claimed responsibility for the December 2006 kidnapping of seven Iranian soldiers in the Zahedan area. It threatened to kill them unless members of the group in Iranian prisons were released. The seven were released a month later, apparently after negotiations through tribal mediators.

Iran's southeast borders Pakistan's Baluchistan province, where Pakistani authorities are battling their own insurgency by Baluchis demanding more autonomy.

Chris Zambelis, a researcher with the Washington-based risk management consultancy Helios Global who has studied Jundallah, said Iranian rebels likely have some connection with those in Pakistan, but the two groups do not necessarily work together to plan attacks.

Iranian authorities have said Jundallah has close ties to "foreign forces" in neighboring Afghanistan, a possible reference to the Al Qaeda terror network.

Iran has also repeatedly accused the United States of backing militants including Jundallah and other ethnic opposition groups to destabilize the government -- charges Washington has denied. The claims have added to the acrimony between Iran and the U.S. over issues like Tehran's nuclear program.