A suicide bomber killed five senior commanders of Iran's Revolutionary Guard, as well as at least 37 others, in a region at the centre of a growing Sunni insurgency, state media reported Sunday.
Among the dead were Gen. Noor Ali Shooshtari, deputy commander of the Guard's ground force, and Rajab Ali Mohammadzadeh, a chief provincial Guard commander for the region, according to the official IRNA news agency.
Local tribal elders were among the others killed in the blast. More than two others were wounded, according to state radio reports.
The commanders were attacked as they travelled to a meeting with tribal elders in the Pishin district in the southeast, near the Pakistan border.
An attacker with explosives around his waist approached the group near the entrance of a sports complex where the meeting was to take place, and blew himself up, IRNA reported.
The semi-official ISNA news agency quoted provincial prosecutor Mohammad Marzieh, who said a militant group from Iran's Sunni Muslim minority known as Jundallah, or Soldiers of God, claimed responsibility.
Jundallah militants accuse Iran's Shiite-dominated government of persecution and have waged a moderate insurgency in the region for years, hitting Guard and Shiite targets.
Iran's President Mahmoud Ahmadinejad relies on support from the Revolutionary Guard. On Sunday, he vowed to retaliate against the perpetrators of the attack.
"The criminals will soon get the response for their anti-human crimes," Ahmadinejad said, according to IRNA. The president also accused "foreigners" of involvement, but did not elaborate.
Iranian officials have been reluctant to open full-scale military operations in the southeastern border zone, fearing it could become a hotspot for violence from al Qaeda and Sunni militants from nearby Pakistan and Afghanistan.
Drug traffickers move opium and other drugs through the badlands. The drugs are a key source of income for the Taliban in Afghanistan and tribes that settle in the region, including members of Jundallah.
Government officials believe Jundallah has received support from both the Taliban and al Qaeda in Pakistan. However, some experts dispute this.
Other officials accused the United States of attempting to spur ethnic and religious minorities in an uprising against the government.
However, U.S. State Department spokesperson Ian Kelly condemned the attacks and said allegations that the U.S. was involved were "completely false."
Iran's parliamentary speaker, Ali Larijani, denounced the attacks and accused the perpetrators of trying to compromise security in the region.
"We express our condolences for their martyrdom. ... The intention of the terrorists was definitely to disrupt security in Sistan-Baluchistan Province," Larijani told parliament in a live radio broadcast.
In an attempt to stem violence in the region, Iranian officials put Sistan-Baluchistan Province under Guard control in April.
In May, Jundallah claimed responsibility for a suicide bombing at a Shiite mosque in Zahedan, capital of Sistan-Baluchistan Province, which killed 25 people
With files from The Associated Press