TEHRAN (Reuters) - Iran's elite Revolutionary Guards promised a "crushing" response to an attack that killed several senior commanders, state television said on Monday, as the death toll from the deadliest such incident in years rose to 42.
Stepping up accusations of Western backing for those behind Sunday's suicide bombing in volatile southeastern Iran, one of the Guards' most high-ranking officers said the United States and Britain trained "terrorists" in neighboring countries.
The attack and allegations of foreign involvement risk overshadowing talks between Iranian and Western officials in Vienna later on Monday intended to help resolve a standoff with the West about Iran's nuclear ambitions.
Pakistan condemned the "ghastly act of terrorism" in an area near its border with the Islamic Republic, and denied suggestions from Tehran that security agents in Pakistan were cooperating with the perpetrators.
The attack in Sistan-Baluchestan province, which killed the deputy head of the Guards' 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 Sunday, state media said a local rebel Sunni group called Jundollah (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."
Sunday's planned meeting in the city of Sarbaz was part of efforts to foster Shi'ite-Sunni unity and the Guards said the attack was aimed at fomenting sectarian strife in the region.
Sistan-Baluchestan is the scene of frequent clashes between security forces, ethnic Baluch Sunni insurgents and heavily-armed drug traffickers.
Jundollah, 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.
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 supported Jundollah to stir up trouble in the border area and has also linked the group to the Sunni Islamist al Qaeda network.
"The base of the terrorists and rebels has not been in Iran. They are trained by America and Britain in some of the neighboring countries," television quoted General Mohammad Pakpour, commander of the Guards' ground forces, as saying.