Militants packed into four cars screeched up to the checkpoint south of Mosul at around 1:30 a.m., attacking it from both sides, said police Brig. Abdel-Karim al-Jubouri. Clashes lasted about 15 minutes, after which all the gunmen escaped, al-Jubouri said.
Six policemen were killed and the other four at the checkpoint were wounded - all men from the local area, he said. Al-Jubouri said it is believed that the assailants - suspected members of the al Qaeda front group the Islamic State of Iraq - sustained some casualties but nobody was left behind.
The attack occurred in the Gayara area south of Mosul, a mostly Sunni Muslim city that includes many ethnic Kurds, located about 225 miles northwest of Baghdad.
The area has seen an increase in violence since U.S. and Iraqi troops launched offensives earlier this year to oust Sunni militants from the Iraqi capital and its surrounding belts. Some al Qaeda-linked insurgents are believed to have fled north, digging into positions in the Sunni-dominated Mosul area.
At least two prison breaks earlier this year also emptied hundreds of suspected insurgents into the streets there.
The Sunni insurgency also has been strong in the volatile Diyala province east of Baghdad, where four civilians were killed and four others injured on Wednesday.
In other developments:
Wednesday's violence came less than a day after insurgents fired rockets or mortars at the sprawling garrison that houses the headquarters of American forces in Iraq, killing one person and wounding 11 coalition soldiers, the U.S. command said.
The command said Tuesday the person killed was a "third country national," meaning someone who is not an American or Iraqi. Most troops stationed at Camp Victory are American, but other coalition soldiers are based at the complex near Baghdad International Airport and workers from other countries are also there.
No further details on the attack were immediately released.
The Iraqi government welcomed Gen. Petraeus' recommendation to keep additional forces in Iraq into this coming year, giving assurances that the need for U.S. military support here would decrease over time.
National Security Adviser Mouwaffak al-Rubaie, reading from a government statement, said the Iraqis believed that "in the near future" the need for U.S. and other coalition forces "will decrease."
"The aim of the Iraqi government is to achieve self-reliance in security as soon as possible, but we still need the support of coalition forces to reach this point," cautioned al-Rubaie, who in the past has often given rosy pictures of Iraq's capabilities.
On Tuesday, Petraeus heard strong rebuttals from some congressional Democrats - some of them presidential contenders - who oppose continued U.S. involvement in the 4 1/2 year war that has claimed at least 3,772 U.S. lives.
Speaking to reporters in Baghdad on Wednesday, al-Rubaie acknowledged disappointment by some U.S. lawmakers at what they saw as the slow pace of progress in Iraq.
"Some of us get tired by the process, either because of the lack of achievement or the personal interests that the many sides have," al-Rubaie said.
"We're going through a tough time and we are facing huge problems, but our persistence is unlimited," he added.
Meanwhile at a wind-swept U.S. military base near the Iranian border, the main points of Petraeus' testimony met with widespread agreement among American soldiers.
Staff Sgt. Matthew Nicholls of the 71st Medical Detachment said the military still needs time to clean up mistakes made after the 2003 invasion, including the need to build an Iraqi army from scratch and to secure the borders.
"I think our initial assessment was too rosy," he said after reading about the hearings while sitting in the library at the recreation center. "It takes time to build an army and I think we should've secured the borders right away."