The chief of Iran’s Revolutionary Guard accused the United States, Britain and Pakistan of having links with the Sunni militants responsible for a suicide bombing.

The bombing killed five senior Guard commanders and 37 others.

Iran’s president said those behind Sunday’s bombing are hiding across the border in Pakistan, and in a phone call with his Pakistani counterpart on Monday he demanded their arrest.

A Sunni rebel group that has waged a low-level insurgency in southeastern Iran to protest what it says is government persecution of an ethnic minority in the region claimed responsibility for the attack. The claim was posted Monday on an Islamic Web site that usually publishes al-Qaida statements. Its authenticity could not be verified.

Jundallah has carried out sporadic kidnappings and attacks in recent years — including targeting the Revolutionary Guard and Shiite civilians. In Sunday’s attack, a suicide bomber with explosives strapped around his waist struck as the Guard commanders were entering a sports complex to meet tribal leaders to discuss Sunni-Shiite cooperation in the Pishin district near the Pakistani border.

Revolutionary Guard chief Gen. Mohammad Ali Jafari said Monday that the Sunni rebel group, known as Jundallah, or Soldiers of God, is at work to disrupt security in Iran and he vowed to deliver a “crushing” response.

“New evidence has been obtained proving the link between yesterday’s terrorist attack and the U.S., British and Pakistani intelligence services,” state TV quoted Jafari as saying. “Evidence shows that U.S., British and Pakistani intelligence supported the group.”

He said the attack was “undoubtedly” planned and ordered by the three nation’s intelligence services and that a delegation would soon travel to Pakistan to present evidence.

Iran often blames Western countries, especially the U.S., of stoking unrest among the country’s religious and ethnic minorities — allegations those nations have denied. Iran has also claimed that Jundallah receives support from al-Qaida and Taliban militants that operate across the border in Pakistan’s Baluchistan province, where Baluchi nationalists have been waging a militant campaign for independence from the Pakistani government.

Several analysts who have studied Jundallah say the group likely receives inspiration and material support from Baluchi nationalists in Pakistan. But they say there is little evidence of an operational relationship between Jundallah and militants, including al-Qaida and the Taliban, that operate across the border.

President Mahmoud Ahmadinejad had harsh words for his Pakistani counterpart, Asif Ali Zardari.

“The presence of terrorist elements in Pakistan is not justifiable and the Pakistani government needs to help arrest and punish the criminals as soon as possible,” state TV quoted Ahmadinejad as telling Zardari Monday.

“We’ve heard that some officers in Pakistan cooperate with the main elements behind such terrorist attacks and we consider it our right to demand these criminals from them,” he was quoted as saying.

Zardari telephoned Ahmadinejad to strongly condemn the suicide attack, said a statement from the Pakistani president’s office.

President Zardari said the incident was “gruesome and barbaric” and bore the “signatures of a cowardly enemy on the run.”

He said both Pakistan and Iran have deep historical ties and he assured that Pakistan will continue to support and cooperate with Iran in curbing militancy and fighting extremism and terrorism.

In a sign of how heated the situation has become, an Iranian lawmaker representing the capital of Iran’s southeastern Sistan-Baluchistan Province called on the Guard to carry out military operations inside Pakistan to root out militants. It’s unclear whether such an operation would be considered.

In the Internet claim of responsibility, a statement in the name of Jundallah said the attack was carried out in “retaliation for the Iranian regime’s crimes against the unarmed people of Baluchistan.”

He was referring to the area populated by ethnic Baluchi tribes, who follow the Sunni branch of Islam and are a minority in predominantly Shiite, Persian Iran.

The statement also identified the man it said carried out the attack as Abdel-Wahed Mohammadi Sarawani, suggesting he is from the small town of Sarawan, 25 miles (40 kilometers) from the Pakistani border.

It also accused the Iranian government of executing many people merely because they are Sunnis or Baluchis.

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

Sunday’s 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 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.

Iran was planning a funeral Monday in Zahedan for nearly all of those killed, state media reports said. A second service will take place in Tehran on Tuesday for one of the commanders, Shooshtari.