A homicide bomber killed five senior commanders of Iran's elite Revolutionary Guard and at least 37 others in an area of southeastern Iran that has been the focus of a growing Sunni insurgency.

The headquarters of Iran's armed forces blamed the bombing on "terrorists" backed by "the Great Satan America and its ally Britain," Fars News Agency was quoted by Reuters.

"Not in the distant future we will take revenge," Iran's statement read, according to Reuters. Iran's forces claim the country "will clear this region from terrorists and criminals."

The United States, however, condemned the attacks on Sunday and denied any involvement. "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 region's top prosecutor was quoted by the semi-official ISNA news agency as saying the Sunni rebel group Jundallah claimed responsibility for the blast. The group accuses Iran's Shiite-dominated government of persecution and has carried out attacks against the Revolutionary Guard and Shiite targets in the southeast.

Iran's parliamentary speaker, Ali Larijani, condemned the assassination of the Guard commanders, saying the bombing was aimed at disrupting security in southeastern Iran. "We express our condolences for their martyrdom. ... The intention of the terrorists was definitely to disrupt security in Sistan-Baluchistan."