Militants killed at least 10 Iraqi policemen in a series of attacks on checkpoints in the West of the country on Sunday, police and local officials said.
Sectarian tensions in Iraq have been amplified by the conflict in neighbouring Syria, where mostly Sunni rebels are fighting to overthrow President Bashar al-Assad who is backed by Shi'ite Iran.
There was no immediate claim of responsibility for the Iraqi attacks, but Sunni militant groups have previously targeted security forces in a campaign to destabilize the Baghdad government, which they reject as illegitimate.
Seven policemen were killed when militants attacked checkpoints and patrols near the western town of Haditha, 190 km (120 miles) northwest of Baghdad, police sources said.
"We were manning a checkpoint when suddenly a group of militants in many vehicles surrounded us and opened fire. Seven of my colleagues were killed instantly," said a policeman at the site.
In Rawa, 260 km (160 miles) northwest of Baghdad, gunmen attacked police checkpoints, the house of a member of the provincial council and a police chief's residence, killing three policemen and wounding two others, police sources said.
The attacks took place in the Sunni heartland of Anbar, where gunmen on Saturday ambushed and kidnapped 10 policemen near the provincial capital of Ramadi, and four members of a government-backed Sunni militia fighters were killed near Falluja city.
When Sunni-Shi'ite bloodshed was at its height in 2006-07, Anbar, which shares a border with Syria, was in the grip of al Qaeda's local affiliate, the Islamic State of Iraq, which has regained strength in recent months.
Minority Sunnis, embittered by Shi'ite dominance since the overthrow of Saddam Hussein by U.S.-led forces in 2003, have been staging street protests against Shi'ite Prime Minister Nuri al-Maliki since December.
A bloody government raid on a Sunni protest camp in Hawija last month ignited a surge of violence. 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 U.N. count, the highest figure in almost five years.