Reporting from Cairo and Tehran - In a brazen attack on Iran's military elite, a suicide bomber today killed five Islamic Revolutionary Guard Corps commanders and 26 others at a gathering of tribal leaders in a southeastern province near the Pakistan border that's known for drug running and religious extremism, according to the official Iranian news agency.

The assault was carried out by a lone man who reportedly disguised himself in tribal dress and detonated an explosives belt at a gymnasium in the city of Pisheen in the Sistan-Baluchistan province, a harsh land plagued by heroin smuggling and ethnic animosities. At least 28 people were wounded in the carnage, images of which were broadcast across a stunned nation.

Iran state-owned Press TV reported that a simultaneous second bombing targeted another group of Revolutionary Guard officers traveling in a convoy near Pisheen. There were no numbers on casualties, and the report could not be independently confirmed.

State media said the Sunni Muslim militant group Jundallah, or Soldiers of God, which operates along the Iran-Pakistan border, claimed responsibility for the attack. The organization, part of a regional Sunni insurgency in Shiite-dominated Iran, has for years killed and kidnapped Iranian soldiers and police officers.

The bomber struck what was to be a reconciliation meeting between Shiite and Sunni tribesmen to calm sectarian tensions in the southeast. The region is a tangle of disenchanted clans and sects that claim they have been persecuted for generations. Jundallah and other groups pose no serious threat to the Iranian government, but they are capable of deadly ambushes against state and Shiite institutions, including a bombing at a mosque in May that killed more than 20 people.

Iran's post-election unrest also may have inspired today's bloodshed. Jundallah had vowed to take revenge on the Revolutionary Guard for cracking down on protestors marching against the disputed June re-election of President Mahmoud Ahmadinejad. The peaceful opposition movement led by vanquished presidential candidate Mir Hossein Mousavi never associated itself with Jundallah, but some analysts suggest the group had plotted the attack to exploit the political turmoil at a time when the Revolutionary Guard is tightening its hold on the country.

"It was a measure to show that IRGC is susceptible and penetrable. A suicide bomber infiltrated a gathering that was supposedly held under tight security because of the presence of the high-ranking IRGC commanders," said Mashaallah Shamsul Waezin , a political analyst in Tehran. "And, secondly, the timing was important because IRGC is associated with the heavy crackdown against post-election protesters, so the terrorist attack can be an intensified echo of public opinion."

The official IRNA news agency said among those killed were Gen. Noor Ali Shooshtari, commander of the Guard's ground force, and Rajab Ali Mohammadzadeh, the chief commander for the region. The other dead reportedly included Guard officers and tribal elders.

The Revolutionary Guard and hard-line politicians blamed "global arrogance" for the bombing and said the U.S. was funding and arming Jundallah and other militant groups to overthrow the Ahmadinejad government. The accusations came the day before officials from the U.S. and other world powers were to meet in Vienna on Monday with Iranian delegates over Tehran's nuclear program.

"There is no doubt that this violent and inhumane act was part of the strategy of foreigners and enemies of the regime and the revolution to destroy unity between Shias and Sunnis and create divisions among the unified ranks of the great Iranian people," said a statement issued by the Revolutionary Guard.

Ali Larijani, the speaker of the Iranian Parliament, agreed.

"We consider the recent terrorist attack to be the result of U.S. action," he said. "This is the sign of America's animosity against our country."

Larijani was quoted by IRNA as telling lawmakers: "The goal of the terrorists is to disturb the security of the Sistan-Baluchistan province. They do not want to have economic progress in this region. But certainly the Guards will react with additional forces to establish security."

A U.S. State Department spokesman denied American involvement.

The U.S. condemns "this act of terrorism and mourns the loss of innocent lives," Reuters quoted spokesman Ian Kelly as saying. "Reports of alleged U.S. involvement are completely false."

Jundallah is mainly made up of ethnic minority Baluchis, who are scattered across Iran, Pakistan and Afghanistan. Press TV termed the group "a Pakistan-based terrorist group closely affiliated with the notorious Al Qaeda organization. The terror ring has carried out countless bombings and other violent attacks in Iran."

jeffrey.fleishman@latimes.com