TEHRAN (Reuters) -- Iran's elite Islamic Revolutionary Guards Corps (IRGC) promised a "crushing" response to an attack that killed several senior commanders, state television has said, as the death toll from the deadliest such incident in years rose to 42.
In neighboring Pakistan, a Foreign Ministry spokesman condemned the October 18 suicide bombing in southeastern Iran near the Pakistani border and denied suggestions from Iran that security agents in Pakistan were cooperating with the perpetrators.
The attack in Sistan-Baluchistan Province, which killed the deputy head of the IRGC ground forces, highlighted deepening instability in a region of mainly Shi'ite Muslim Iran bordering Pakistan and Afghanistan.
Many minority Sunnis live in the impoverished area, which has seen an upsurge in bombings and other violence.
On October 18, state media said a local rebel Sunni group called Jundallah (God's Soldiers) claimed responsibility for the attack, which also wounded many people ahead of a meeting between Guards officers and tribal chiefs.
"At least 42 killed, dozens hurt in southeast Iran terrorist attack," Press TV, Iran's state English-language television station, said.
It said tribal leaders and civilians were also among the victims and that the Guards had promised a "crushing response."
On October 19, IRGC chief Major General Mohammad Ali Jafari said, "Behind this scene are the American and British intelligence apparatus and there will have to be retaliatory measures to punish them."
The October 18 planned meeting in the city of Sarbaz was part of efforts to foster Shi'ite-Sunni unity and the IRGC said the attack was aimed at fomenting sectarian strife in the region. About 10 senior tribal figures died in the incident.
Sistan-Baluchistan is the scene of frequent clashes between security forces, ethnic Baluch Sunni insurgents and heavily-armed drug traffickers.
Jundallah, which accuses Iran's Shi'ite-led government of discrimination against Sunnis in the remote desert region, has been blamed for many deadly incidents over the last few years.
'Ghastly Act Of Terrorism'
Iranian officials also accused the United States and Britain of involvement, a charge rejected by Washington, which also condemned the attack. Iran has in the past said Washington backed Jundallah to stir trouble in the border area and has also linked the group to the Sunni Islamist Al-Qaeda network.
The October 18 attack was the deadliest such incident in Iran since its 1980-88 war with Iraq. A bombing of a mosque in Sistan-Baluchistan in May, reportedly also claimed by Jundallah, killed 25 people.
The attack and allegations of foreign involvement risk overshadowing talks between Iranian and Western officials in Vienna later on October 19 intended to help resolve a standoff with the West about Iran's nuclear ambitions.
Iran's President Mahmud Ahmadinejad was quoted as saying on October 18 that security agents in Pakistan were cooperating with the militants behind the bombing.
"We were informed that some security agents in Pakistan are cooperating with the main elements of this terrorist incident.... We regard it as our right to demand these criminals from them," Ahmadinejad said, Fars news agency reported.
Pakistan's Foreign Ministry spokesman Abdul Basit told the "Daily Times" newspaper: "Pakistan is not involved in terrorist activities...we are striving to eradicate this menace."
Pakistan's Prime Minister Yousaf Raza Gilani strongly condemned the "ghastly act of terrorism" in Iran, his office said.
Pakistan has in the past backed Sunni Muslim armed groups, particularly in Afghanistan in the 1980s against Soviet occupiers. It also supported militants who have been battling Indian security forces in the disputed Kashmir region. Both Afghanistan and India say Pakistan has maintained links to some militant groups.
Relations between Iran and Pakistan have been generally good in recent years and the neighbors are cooperating on plans to build a natural-gas pipeline link.
But Iran has in the past accused Pakistan of hosting Jundallah members, Iranian state television said.
Some analysts believe Jundallah has evolved through shifting alliances with various parties, including the Taliban and Pakistan's ISI intelligence service, who saw the group as a tool against Iran.