The United Nations warned on Friday that Iraq is at a "crossroads" and appealed for restraint, as a bloody four-day wave of violence, including multiple attacks at mosques, killed 195 people.

"I call on the conscience of all religious and political leaders not to let anger win over peace, and to use their wisdom, because the country is at a crossroads," UN envoy Martin Kobler said in a statement.

The call came a day after Prime Minister Nuri al-Maliki warned of a return to "sectarian civil war."

Abdulghafur al-Samarraie and Saleh al-Haidari, leading clerics who respectively head the Sunni and Shiite religious endowments, have also jointly warned against sectarian strife and called for top politicians to meet at a Baghdad mosque on Friday.

But an official from the Sunni endowment said the meeting was cancelled.

Bombs exploded at three Sunni mosques in Baghdad and a fourth north of the capital on Friday, killing at least four people and wounding 50, after more than a dozen people were killed in attacks at Sunni mosques on Tuesday.

Iraqi security forces, meanwhile, began moving back into the northern town of Sulaiman Bek after gunmen who seized it withdrew.

The gunmen pulled out of the predominantly Sunni Turkmen town in Salaheddin province under a deal worked out by tribal leaders and government officials, local official Shalal Abdul Baban and municipal council deputy chief Ahmed Aziz said.

The gunmen had swarmed into Sulaiman Bek on Wednesday after deadly clashes with security forces, who pulled back as residents fled.

Baban also said that helicopter fire wounded six people on the roof of a house in the town early on Friday.

Army Staff General Ali Ghaidan Majeed told AFP on Thursday that the gunmen in Sulaiman Bek, who he said numbered about 175, had been given 48 hours to withdraw or face attack.

The gunmen's seizure of the town came amid a surge of violence which began on Tuesday when security forces moved in against anti-government protesters near the Sunni Arab northern town of Hawijah, sparking clashes that left 53 people dead.

Dozens more were killed in subsequent unrest, much but not all of it apparently linked to Tuesday's clashes, bringing the death toll to 195 by Friday.

The violence is the deadliest so far linked to demonstrations that broke out in Sunni areas of the Shiite-majority country more than four months ago.

The protesters have called for the resignation of Maliki, a Shiite, and railed against authorities for allegedly targeting their community.

Seven gunmen died carrying out three separate attacks on security forces south of the northern city of Kirkuk on Friday, a high-ranking army officer and a medical source said.

Gunmen also killed a soldier and wounded two police in an attack on a checkpoint in Al-Sharqat, north of the capital, late on Thursday, a police colonel and a doctor said.

And three hours of fighting in Fallujah, west of Baghdad, killed three federal police and wounded six, police Lieutenant Colonel Yassir Hamid al-Jumaili and a doctor said.

The clashes saw gunmen take control of three checkpoints on the outskirts of the overwhelmingly Sunni Arab city after they were abandoned by federal police, Jumaili said.

He said they then turned the checkpoints over to local police, who returned them to federal police on Friday.