The United States condemned a suicide bombing that killed six senior Iranian Revolutionary Guards commanders and denied it had anything to do with it.

"We condemn this act of terrorism and mourn the loss of innocent lives. Reports of alleged US involvement are completely false," US State Department spokesman Ian Kelly said in a brief statement.

Sunday's Attack 6 Revolutionary Guard commanders killed in Iran bombing News agencies IRNA reports suicide bombing near Iran's border with Pakistan kills dozens, including a number of senior elite Revolutionary Guard commanders; dozens more wounded. Tehran accuses Britain of involvement in attack 6 Revolutionary Guard commanders killed in Iran bombing

Meanwhile, Iranian President Mahmoud Ahmadinejad ordered authorities to swiftly track down and punish those behind Sunday's suicide attack in the country's volatile southeast, the official IRNA news agency reported.

Ahmadinejad said "the criminals who committed ... crimes against humanity ... will be seriously dealt with," IRNA reported.

The attack highlighted deepening instability in the Islamic Republic's southeast bordering Pakistan and Afghanistan, where many of Iran's minority Sunnis live and which has seen a spate of deadly bombings and other violence in the last few years.

State media said a local rebel Sunni group called Jundollah (God's soldiers) claimed responsibility for the attack, the deadliest on the elite Revolutionary Guards in recent years, which also wounded some 30 people at a meeting of tribal chiefs.

The southeastern province of Sistan-Baluchestan is the scene of frequent clashes between security forces, ethnic Baluch Sunni insurgents and heavily-armed drug traffickers.

The region has also been the focus of attacks in recent years by Jundollah, which accuses Iran's Shiite-led government of discrimination. Iranian officials have accused Jundollah of receiving backing from al-Qaeda and the United States.

Iran's armed forces accused the United States and Britain of involvement in Sunday's attack, the semi-official Fars News Agency reported.

The headquarters of the armed forces blamed the bombing on "terrorists" backed by "the Great Satan America and its ally Britain".

"Not in the distant future we (Iran) will take revenge ... and Baluchis will clear this region from terrorists and criminals," Fars quoted a statement as saying, referring to the inhabitants of Sistan-Baluchestan province, where the attack took place.

Revenge?

The deputy head of the Guards' ground forces, General Nourali Shoushtari, and its commander in Sistan-Baluchestan province, General Rajabali Mohammadzadeh, were among the killed.

"Rigi's terrorist group has claimed responsibility for the attack," said state television, referring to Abdolmalek Rigi, leader of Jundollah which is linked by some analysts to the Taliban in neighbouring Pakistan.

"Not in the distant future we (Iran) will take revenge ... and Baluchis will clear this region from terrorists and criminals," Fars quoted the armed forces statement as saying, referring to the inhabitants of Sistan-Baluchestan province, where the attack took place.

State television showed footage of three bodies covered with blood-stained clothing and of wounded people being taken to hospital. Glass shards and other debris were scattered at the scene of the attack.

Predominantly Shiite Muslim Iran accuses the United States of backing Jundollah to stir trouble in sensitive border areas, a charge that Washington denies. Tehran has also linked the group to the Sunni Islamist al-Qaeda network.

Most people in Sistan-Baluchestan are Sunni Muslims and ethnic Baluchis. Iran rejects allegations by Western rights groups that it discriminates against ethnic and religious minorities.

The Revolutionary Guards is an elite force seen as fiercely loyal to Iran's supreme leader, Ayatollah Ali Khamenei. Its power and resources have increased in recent years. It handles security in key border areas.