A suicide bomber disguised as a mourner killed at least 22 people inside a Shia Muslim mosque in northern Iraq when he detonated his explosives in the middle of a crowded funeral ceremony today.

The attack on a religious target came with Shia Prime Minister Nuri al-Maliki facing pressure from mass Sunni protests that are worsening fears that Iraq could return to widespread sectarian confrontation.

Dressed in a suit, the bomber mingled with mourners before the blast at the Saif al Shuhada - Sword of the Martyrs - mosque in Tuz Khurmato city at a ceremony for a Shia ethnic Turkman.

"I was sitting in the seats at the back when all of sudden I heard the sound of a huge explosion. Thank God I was behind because people in front of me saved me with their bodies," said Abbas Qadir Mohammed, 35, one of the wounded.

Rigot Mohammed, an Iraqi army spokesman, said at least 22 people were killed and more than 50 more wounded in the blast in the religiously and ethnically mixed city 170km north of the capital Baghdad.

Mr Maliki is struggling to calm weeks of street protests by Sunni Muslims while his fragile government, split among the Shia majority, Sunnis and ethnic Kurds, is deadlocked in a crisis over power sharing.

The attack on Tuz Khurmato was the fourth suicide bombing in Iraq in a week, including one that killed a Sunni lawmaker in a town where protesters have been calling for Mr Maliki to step down.

Al-Qaeda claimed responsibility for that bombing.

Sunni unrest and renewed violence in Iraq is compounding fears that the war in neighbouring Syria, where Sunni rebels are battling to topple Shia Iran's ally Bashar al-Assad, will upset Iraq's own fragile sectarian and ethnic mix.