Two Iraqi policemen opened fire Tuesday during a U.S. military inspection visit in northern Iraq, killing Emmert and an interpreter in an attack that deepened worries of possible infiltration of security forces battling insurgents in their last major base.
The shooting at a police outpost in Mosul wounded three other U.S. soldiers. It was the fourth attack in the region since late 2007 with suspected links to Iraqi security units, which have struggled to uproot al-Qaida from strongholds in Iraq's third-largest city.
Any serious breaches in the Iraqi force could be a particular blow in the Mosul region — where the U.S. military is light and commanders have been generally unable to spawn the type of tribal militia uprisings that helped break insurgent control in other areas of Iraq. 
The military statement gave no other details, saying the attack was under investigation. The two policemen began shooting as the Americans toured an Iraqi police unit guarding a key bridge in Mosul, about 225 miles northwest of Baghdad, police spokesman Brig. Gen. Saeed al-Jubouri said.
The attackers then fled in a car from the headquarters, a collection of concrete towers and bunkers.
Al-Jubouri denied reports that the gunmen could have been insurgents dressed in police uniforms — a tactic used before in suicide bombings and attacks. He identified them as a sergeant major and a rank-and-file officer from Shura, a village about 25 miles south of Mosul.
Iraqi troops were sent to the village, but there was no immediate report the suspects had been located.
"Absolutely these were policeman," al-Jubouri told The Associated Press.
The Mosul area has been the focus of repeated Iraqi-led campaigns to cripple al-Qaida in Iraq and its backers. More than 100 suspects have been rounded up during a crackdown that began last week.
But insurgents remain entrenched and capable of striking back. Mosul also could take on a greater strategic importance under a plan to withdraw most troops from Iraq by August 2010, according to Washington officials who expect President Barack Obama to make the announcement this week.
U.S. and Iraqi forces could press harder to dismantle insurgent networks in Mosul before American backup is gone.
Earlier this month, a suicide car bomber struck a U.S. patrol in Mosul, killing four American soldiers and an Iraqi interpreter in the deadliest single attack against U.S. forces in nine months.
Some attacks may have been inside jobs. On Nov. 25, two U.S. troops — a Marine and a soldier on a transition team working with the Iraqis — were killed when a gunman in an Iraqi army uniform opened fire while they were distributing aid southwest of Mosul.
It remains unclear whether the attacker was a soldier or posing as a serviceman. Earlier that month, on Nov. 12, an Iraqi soldier ambushed U.S. soldiers in a courtyard of an Iraqi military base in an Arab neighborhood in Mosul.
Two Americans were killed and six wounded before the attacker was killed in the gunbattle that followed.
