Deadly violence in Iraq has spilled into a fourth day, with reports that seven more people killed and three more injured, amid fears over a new round of sectarian bloodshed.

Two police officers were killed on Saturday after an improvised device exploded at a federal police station south of Mosul, a Sunni Muslim-majority area in the country's north, Al Jazeera's Omar Al Saleh, reporting from Erbil, said.

He said one soldier was killed west of Mosul in a similar attack, which also wounded three soldiers.

Reuters news agency reported that four people were killed in a separate bomb attack in Fallujah, 65km west of Baghdad.

On Friday, more than 70 people were killed in bombings in majority Sunni Muslim districts in Baghdad and surrounding areas, in what has been noted as the deadliest day in Iraq in more than eight months.

The ongoing violence is reminiscent of the retaliatory attacks between the two Islamic branches in 2006-2007 that claimed tens of thousands of lives.

Martin Kobler, the UN envoy to the country, called on Iraqi leaders to stop the violence. "It is the responsibility of all leaders to stop the bloodshed in this country and to protect their citizens," he said in a statement on Friday.

"Small children are burned alive in cars. Worshippers are cut down outside their own mosques. This is beyond unacceptable."

Friday's violence

In the deadliest attack on Friday, twin bombings near a Sunni mosque in Baquba, north of Baghdad, killed 41 people and injured dozens.

One bomb exploded as worshippers were departing the Saria mosque while a second went off after people gathered at the scene of the first blast, police said.

No group claimed responsibility for the attack.

On Friday in Baghdad, a bomb exploded near a shopping centre during evening rush hour in the mainly Sunni neighbourhood of Amariyah, killing at least 12 people and wounding 32.

That was followed by another bomb in a commercial district in Dora, another Sunni neighbourhood, which killed two people and wounded 22, according to officials.

In another attack, a roadside bomb exploded during a Sunni funeral procession in Madain, south of Baghdad, killing eight mourners and wounding 11, police said.

An explosion also struck a cafe in Fallujah, killing two people and wounding nine, according to police and hospital officials.

Sectarian nature

A day earlier, attacks targeted Shias in several locations. Our correspondent said the sectarian nature of recent attacks was worrying Iraqis.

"You have attacks on Shia worshippers, you have attacks on Sunni worshippers. It appears that whoever is behind those attacks wants to ignite sectarian strife," he said.

"It's an indication that security conditions are really going downhill in this country. There is a huge and growing sense of fear among Iraqis."

Tension has flared since Sunnis began protesting 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.