The attack, which also left 75 people wounded, is likely to heighten tensions as Iraq grapples with a political crisis and more than a month of protests in Sunni-majority areas that have hardened opposition against Shiite prime minister Nuri al-Maliki.

No group claimed responsibility, but militants often launch attacks in a bid to destabilise the government and push Iraq back towards the sectarian violence that blighted it from 2005 to 2008.

The militant struck at the Sayid al-Shuhada mosque in Tuz Khurmatu, 175 kilometres (110 miles) north of Baghdad, and targeted the funeral of a relative of a politician who was killed by gunmen a day earlier.

Niyazi Moamer Oghlu, the secretary general of the provincial council of Salaheddin, which surrounds Tuz Khurmatu, put the toll from the attack at 42 dead and 75 wounded.

"Corpses are on the ground of the Husseiniyah (Shiite mosque)," said Shallal Abdul, mayor of Tuz Khurmatu. "The suicide bomber managed to enter and blow himself up in the middle of the mourners."

Among the wounded were officials and tribal leaders, including Ali Hashem Oghlu, the deputy chief of the Iraqi Turkman Front and a provincial councillor in Salaheddin.

The funeral had been for Mukhtar's brother-in-law, who was shot dead in Tuz on Tuesday afternoon.

Wednesday's suicide bomb came after a wave of attacks a day earlier killed 26 people and wounded dozens more, shattering a relative calm after a spate of deadly violence last week.