TEHRAN, Iran — A suicide bomber killed five senior commanders of the powerful Revolutionary Guard and at least 37 others today near the Pakistani border in the heartland of a potentially escalating Sunni insurgency.

The attack — which also left dozens wounded — was the most high-profile strike against security forces in an outlaw region of armed tribal groups, drug smugglers and Sunni rebels known as Jundallah, or Soldiers of God.

President Mahmoud Ahmadinejad promised sharp retaliation. But a sweeping offensive by authorities is unlikely.

Iranian officials have been reluctant to open full-scale military operations in the southeastern border zone, fearing it could become a hotspot for sectarian violence with the potential to draw in al-Qaida and Sunni militants from nearby Pakistan and Afghanistan.

The region’s top prosecutor, Mohammad Marzieh, was quoted by the semi-official ISNA news agency as saying Jundallah claimed responsibility for the blast in the Pishin district near the Pakistani border.

There was no immediate statement directly from the group, which has carried out sporadic kidnappings and attacks in recent years — including targeting the Revolutionary Guard — to press their claims of persecution in the Shiite government and officials.

In May, Jundallah said it sent a suicide bomber into a Shiite mosque in the southeastern city of Zahedan, killing 25 worshippers.

The latest attack, however, would mark the group’s highest-level target. It also raised questions about how the attacker breached security around such a top delegation from the Revolutionary Guard, the country’s strongest military force, which is directly linked to the ruling clerics under Supreme Leader Ayatollah Ali Khamenei.

The official Islamic Republic News Agency said the victims included the deputy commander of the Guard’s ground forces, Gen. Noor Ali Shooshtari, as well as a chief provincial Guard commander, Rajab Ali Mohammadzadeh. The others killed were Guard members or tribal leaders, it said.

The agency quoted the provincial forensics director, Abbas Amian, as saying 42 bodies had been handed over to his department.

More than two dozen others were wounded, state radio reported.

The commanders were entering a sports complex to meet tribal leaders to discuss Sunni-Shiite cooperation when the attacker detonated a belt fitted with explosives, IRNA said.

Ahmadinejad — who counts on support from the Revolutionary Guard — vowed to strike back.

“The criminals will soon get the response for their inhuman crimes,” IRNA quoted him as saying.