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 Republic of Iran, 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.
On Sunday, state media said a local 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.
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.
Jundollah accuses Iran's Shi'ite-led government of discrimination against Sunnis in the remote desert region.
Iranian officials also accused the United States and Britain of involvement, a charge rejected by Washington. Iran has in the past said Washington supported Jundollah to stir up trouble in the border area.
Pro-government daily Kayhan also pointed the finger at Israel, describing the attack as the "new crime" of the Jewish state's intelligence agency Mossad.
Sunday's attack was the deadliest such incident in Iran since its 1980-88 war with Iraq. A bombing of a mosque in Sistan-Baluchestan last May, reportedly also claimed by Jundollah, killed 25 people.
Russian cooperation
The attack raised tension between Iran and major powers ahead of nuclear talks in Vienna. An Iranian official said that Tehran will further enrich uranium itself if nuclear talks fail with the U.N. watchdog, Russia, France and the United States.
The talks will discuss sending Iran's low enriched uranium abroad for further processing and return to Tehran.
The Guards force, whose influence has increased since Ahmadinejad came to power in 2005, played a key role in suppressing the street protests after the election.
Russian President Dmitry Medvedev offered Moscow's cooperation "in fighting terrorism and extremism", in a letter to Ahmadinejad, Medvedev's press service said.
"We are ready to cooperate with Iran in countering these threats," he wrote, expressing condolences for the attack.
Ahmadinejad was quoted as saying on Sunday that security agents in Pakistan were cooperating with the militants behind the bombing.
Pakistan's Foreign Ministry spokesman Abdul Basit told the Daily Times newspaper: "Pakistan is not involved in terrorist activities..."
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 said Jundollah members have been operating out of Pakistan.
PHOTO CAPTION
A wounded man arriving at a hospital in the southeastern Iranian city of Pisheen, near the border with Pakistan.
Agencies