Violence in Iraq killed 27 people on Tuesday as the United Nations warned that an upsurge in sectarian attacks threatens to displace more civilians from their homes.

Insurgents battled police and troops west and north of Baghdad.

In Anbar province west of the capital, militants attacked two police stations and a local official's house in the towns of Rawa and Aana near the main highway from Baghdad to the Syrian border, killing seven police and the official's brother, medical and security sources said.

Deputy Interior Minister Adnan al-Assadi told journalists a large group of militants had attacked Aana, seeking to take control of security force positions.

Security forces killed six of the militants, Assadi said, adding that SWAT units had been deployed to the area.

North of Baghdad, two soldiers and four militants died in clashes in the Hamreen area, officers said.

A helicopter pilot was wounded by gunfire in the operation, during which two militants were arrested and weapons seized, army Staff Lieutenant General Abdulamir al-Zaidi told AFP.

Two officers said a helicopter had been shot down, but Zaidi insisted that it was able to return to base.

Three people were killed in the northern province of Nineveh and two in Babil province, south of Baghdad.

In the capital, a car bomb killed at least two people and wounded seven more.

The UN refugee agency said it was "increasingly concerned about the situation in Iraq, where recent waves of sectarian violence threaten to spark new internal displacement of Iraqis fleeing bombings and other attacks."

This year, "bombings and rising sectarian tensions have displaced some 5,000 Iraqis, with people mostly fleeing from Baghdad into Anbar and Salaheddin governorates, as well as causing displacement within Diyala and Nineveh governorates," agency spokeswoman Melissa Fleming said in a statement.

There are already "more than 1.13 million internally displaced people... inside Iraq who fled their homes to escape intense sectarian violence from 2006-2008," she added.

The Tuesday violence came after four days of sectarian attacks that have raised the spectre of a return to the all-out Sunni-Shiite conflict that peaked in 2006-2007 and killed tens of thousands of people.

A bombing against Sunni mourners in Baghdad on Monday killed 15 people, while another at a Sunni funeral the day before killed 12.

Those attacks were preceded by bombings targeting Shiite mourners in the capital on Saturday that killed 73, and two blasts at a Sunni mosque north of Baghdad in which 18 died on Friday.

Prime Minister Nuri al-Maliki said on Monday that attacks in Iraq aimed to "reignite sectarian strife" and divide the country.

On Tuesday, the cabinet agreed to allocate an aircraft to transport people wounded in recent attacks abroad for treatment, Maliki's website said.

With the latest violence, more than 630 people have been killed this month and over 4,450 since the beginning of the year, according to AFP figures based on security and medical sources.