The chief of Iran's powerful Revolutionary Guard accused the United States, Britain and Pakistan on Monday of having links with Sunni militants responsible for a suicide bombing that 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. The accusations put more strain on the tense relationship that Iran and Pakistan have had for years over the issue of Islamic extremism. Monday's statements marked the first time Iran has publicly accused its neighbor's intelligence service of supporting the Sunni rebel group known as Jundallah, or Soldiers of God. Jundallah, which emerged in 2002 in Iran's remote and mountainous southeast, has waged a low-level insurgency there to protest what it says is government persecution of the Baluchi ethnic minority. Baluchis follow the Sunni branch of Islam and are a minority in predominantly Shiite, Persian Iran. A claim of responsibility in the name of the group was posted Monday on an Islamic Web site that usually publishes al-Qaida statements. The posting, whose authenticity could not be verified, made no mention of any assistance from foreign powers. The group 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 senior 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 vowed Monday to deliver a "crushing" response. "New evidence has been obtained proving the link between yesterday's terrorist attack and the US, British and Pakistani intelligence services," state TV quoted Jafari as saying. 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 accuses Western countries, especially the US, 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 who operate across the border in Pakistan's Baluchistan province, where Baluchi nationalists have been waging a militant campaign for independence from the Pakistani government. Iran's Jundallah, by contrast, does not appear to seek independence, but rather improved rights for the area's Baluchi people. In 2007, the group adopted a more secular name, the Iranian Popular Resistance Movement, and said it did not depend entirely on armed struggle, but also on political and peaceful efforts to achieve Baluchi rights. The group is still widely referred to by its previous name. 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 Monday 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. "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 pledged 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." 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. 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. Funerals were held Monday in Zahedan and Pishin for many of those killed, state media reports said. State TV broadcast images of thousands of mourners and coffins being placed on the backs of trucks. Some local Sunni tribal leaders condemned the attack and appealed for unity between Sunnis and Shiites. A second service will take place in Teheran on Tuesday for one of the commanders, Shooshtari.