Iranian state media report that at least 42 people have been killed in southeastern Iran in an attack against the country's Islamic Revolutionary Guards Corps (IRGC).
The reports say a suicide bomber blew himself up in the Pishin area of the Sistan-Baluchistan Province, killing six Revolutionary Guards members, including two high-ranking commanders, as well as tribal elders and civilians.
Iran's semi-official Fars news agency has identified the two commanders as the deputy head of the IRGC's ground forces, General Nurali Shushtari, and the IRGC's commander in Sistan-Baluchistan, General Rajabali Mohammadzadeh.
Iranian officials are accusing the United States and Britain of backing the perpetrators of the suicide attack, which took place as Revolutionary Guards commanders were meeting with tribal elders.
The United States condemned the attack and denied any connection to it. "We condemn this act of terrorism and mourn the loss of innocent lives. Reports of alleged U.S. involvement are completely false," U.S. State Department spokesman Ian Kelly said in a brief statement.
The attack was likely to raise tensions with the West, coming on the eve of a meeting in Vienna between Iranian and Western officials to discuss the county's nuclear program.
It could also lead to increased security measures in Sistan-Baluchistan Province, which is the scene of frequent clashes between security forces, drug traffickers, and rebel groups.
London-based analyst Abdol Sattar Doshoki told RFE/RL's Radio Farda that the Islamic republic could use the attack in order to increase pressure on its opponents.
"Unfortunately we have a regime that wants to solve everything and push its plans through military means," Doshoki said. "This results in the spread of violence in Tehran and also Baluchistan."‘Foreign Elements’
The IRGC said in a statement that foreign elements backed by the United States are to blame for the deadly attack. Iran's state television quoted "informed sources" as saying that Britain was directly involved in the attack.
General Nourali Shoushtari was among the high-ranking victims.
Parliament speaker Ali Larijani also said that the United States was implicated, adding that the attack has "burned" the hand of U.S. President Barack Obama.
Iranian state television reports that the Sunni rebel group Jundallah has claimed responsibility for the attack.
A journalist based in the region, Emadedin Mazari, the editor in chief of the "Sobhe Zahedan" weekly, finds Jundallah's claim credible. The group has been behind a series of deadly attacks in Sistan-Baluchistan. Iran has in the past accused the United States and Britain of supporting the group to create instability in the country.
"Today's attack is very similar, in its form and nature, with previous attacks in the region," Mazari says. "Therefore it’s highly likely that it’s the work of the terrorist group led by Abdolmalek Rigi," he said, referring to the leader of Jundallah.
Mazari says the attack was a move by the rebel group to disrupt a new plan by the Revolutionary Guards aimed at involving different tribes in improving security in the region.
Mazari told RFE/RL that Jundallah wanted to prevent any rapprochement between the Baluch Sunni minority and the establishment.
"Commander Shushtari had started this new initiative to get in touch with tribal elders," Mazari says. "He seemed to really believe in it; he wanted to bring security through the elders and the people themselves."
Hours after the attack, Iran's Foreign Ministry summoned a senior Pakistani diplomat in Tehran.
"Iran's Foreign Ministry says there is evidence the perpetrators of this attack came to Iran from Pakistan," Press TV reported. "The Pakistani official assured Tehran that his country would take all measures to secure its border with Iran."
Iran has in the past accused Pakistan of hosting members of Jundallah, Press TV said.
The IRGC said in a statement that the attack is in line with the “evil” strategy of foreigners to create discord between Shi'a and Sunnis.
Mazari says the attack will have political, social, and economic consequences for the region, which is among the most deprived in Iran.
Britain condemned the "terrorist attack" in Sistan-Baluchistan and the loss of life that it caused.
Iran's Interior Ministry said the perpetrators of the attack will be arrested “very soon” and punished.