Story highlights Suicide car bombing kills four police officers in al-Rutba

Gunmen later kill three other police officers at security checkpoints in the town

Also Tuesday, car bomb kills one person, injures 11 others in central Iraqi town of Musayyib

Seven police officers were killed and nine were injured Tuesday in a series of attacks at security checkpoints in the western Iraqi province of Anbar, police said.

The attacks happened in the town of al-Rutba, a predominantly Sunni Muslim community that for a few years was an al Qaeda stronghold after the 2003 U.S-led invasion of the country.

In Tuesday's first attack, a suicide car bombing at a police checkpoint in northern al-Rutba killed four police officers and injured three others, said police officials in Ramadi, the provincial capital.

Gunmen later attacked several security checkpoints in the town, killing three police officers and wounding six, police said.

Information about the attackers' casualties, beyond the suicide bomber, wasn't available. Al-Rutba is about 435 kilometers (270 miles) west of the country's capital, Baghdad.

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Also Tuesday, a car bomb exploded near a busy market in the central Iraqi town of Musayyib in Babil province, killing one person and injured 11, police in Baghdad said.

Musayyib, a largely Shiite town, is about 70 kilometers (43 miles) south of Baghdad.

Iraq has seen a sharp increase in tension between its Shiite and Sunni populations since April, when security forces raided a site used by Sunni protesters to demonstrate against the Shiite-led government.

Sunnis, who represent a minority of Iraqis, have felt politically marginalized since the overthrow of Saddam Hussein in 2003. Shiites make up a majority of Iraqis.

So far in 2013, more than 6,000 people have been killed in Iraq. More than 350 of those deaths came this month, and almost 1,000 happened in September.