An Iraqi Shiite paramilitary group says a roadside bomb has hit a bus carrying its fighters in eastern Iraq, killing seven people and wounding 26.

The Popular Mobilization Forces said in a statement that the bomb hit the bus in the eastern town of Balad Ruz, while traveling from the southern province of Basra.

No one immediately claimed responsibility for the attack. The Sunni Islamic State group has targeted Shiite groups in the past.

IS, which seized Iraqi cities and declared a self-styled Islamic caliphate in territories it controls in Syria and Iraq, was formally declared defeated in Iraq following a three-year bloody battle that left tens of thousands dead and Iraqi cities in ruins.

The extremist group sleeper cells continue to launch attacks in different parts of Iraq.