The death toll in Iraq from four consecutive days of violence has reached at least 140 people, stirring fears that rising sectarian conflicts could lead the country into civil war.

Many Iraqis were in mourning on Sunday amid simmering tensions between the Sunni minority and Shia majority despite increased security patrols.

In Baghdad, the presence of SWAT teams, army, police officers and mobile checkpoints has increased in several areas.

Officers are searching cars and roads for suspicious packages.

"The situation in Baghdad appears to be relatively calm but it remains very tense," Al Jazeera's Omar Al Saleh, reporting from Erbil, said

On Saturday, attacks killed 16 people, including a police officer, his wife and two children, while armed men abducted 10 policemen, officials said.

In Anbar, four state-backed so-called Sahwa (Awakening) fighters were killed in an attack on their headquarters.

The Sahwa are Sunni Arabs who joined forces with the US military to fight al-Qaeda's Iraq branch at the height of the country's conflict.

Policemen ambushed

Armed men also ambushed and abducted 10 Sunni policemen near Ramadi, the capital of Anbar, a Sunni heartland bordering Syria.

"In Ramadi, which is west of Baghdad, tribesmen are on alert ... the army chief said he won't listen to calls made by the tribes for them [the army] to leave Anbar," Al Jazeera's Saleh said.

There was no immediate claim of responsibility for the attacks.

"Iraq is facing its worst crisis since the occupying US forces withdrew over a year ago ... many Iraqis fear the sectarian nature of the recent attacks means the country is heading towards a civil war," he said.

More than 70 people were killed in bombings on Friday in majority Sunni districts in Baghdad and surrounding areas, in what was noted as the deadliest day in Iraq in more than eight months.

Ongoing protests by Sunnis continue, with many demonstrating against what they say is mistreatment at the hands of the mainly Shia-led government, including random detentions and neglect.

The protests, which began in December, have largely been peaceful, but the number of attacks rose sharply after a deadly security crackdown on a Sunni protest camp in the country's north on April 23.

So far in May, more than 300 people have been killed in the violence. The death toll for this year is around 1,500 people.

Monthly death tolls are well below those of 2006-07, when they sometimes topped 3,000, but more than 700 were killed in April by a UN count, the highest figure in almost five years.