TEHRAN  A Sunni militant group whose leader was recently executed by Iranian authorities claimed responsibility on Friday for one of the deadliest terrorist attacks Iran has seen in years: a double suicide bombing outside a mosque that killed 26 people and wounded 300.

The bombing underscored the continuing threat of religious and ethnic violence in Iran, which is unrelated to the political upheavals of the past year. The victims included members of the powerful Islamic Revolutionary Guards Corps, officials said, which the militant group Jundallah has singled out repeatedly in the past.

The group claims to be fighting on behalf of Sunni Muslim members of the Baluch ethnic group in Iran and Pakistan and has been a thorn in the side of Iran’s security services for years, repeatedly bombing Zahedan and other southeastern cities. It claimed responsibility for an attack in October 2009 that killed 40 people, including 15 members of the Revolutionary Guards.

In an Internet statement, Jundallah said two of its “faithful and brave sons” had detonated their bombs at a gathering of the Revolutionary Guards at a religious meeting hall in Zahedan on Thursday that commemorated the organization.