The shooting at a police outpost in central Mosul — which left three other U.S. soldiers wounded — was the fourth attack in the region since late 2007 with suspected links to Iraqi security units, which have struggled to uproot al-Qaida in Iraq from strongholds in Iraq's third-largest city.

Any serious breaches in 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 two policemen began shooting as the Americans toured an Iraqi police unit guarding a key bridge in Mosul, about 225 miles (360 kilometers) 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.

The U.S. military said one interpreter was killed in a small-arms attack and a soldier died later of wounds. Three other soldiers and another interpreter were wounded. The military statement gave no other details, including who did the shooting, saying the attack was still under investigation.

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 rank-and-file officer from Shura, a village about 25 miles (40 kilometers) south of Mosul. Iraqi troops were immediately sent to the village, but there was no immediate reports the suspects were 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.

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.

Other attacks have been waged as possible 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 a Arab neighborhood in Mosul. Two Americans were killed and six wounded before the attacker was killed in the gunbattle.

In December 2007, an Iraqi soldier shot and killed a U.S. captain and a sergeant during a joint operation in Mosul.

In Baghdad, a prominent Sunni politician rallied behind a lawmaker accused of running a private terror cell and demanded full probes into Shiites and others parliament members suspected of links to violence.

Saleh al-Mutlaq, who leads a Sunni bloc, has used the allegations against one of his former political allies to press Sunni claims that the Shiite-led government is not doing enough to investigate Shiite abuses committed during the height of Iraq's sectarian bloodshed.

"We demand that all files against other lawmakers be opened and investigated by a special parliament committee that is free from government pressures," he told a news conference.

The demand could further complicate the crisis in Iraq's parliament, which has been in gridlock since December over disputes on selecting a new speaker. The impasse has left lawmakers unable to take up pressing issues such as U.S.-backed proposals to enact a law that covers foreign oil industry investment and revenue distribution.

Al-Mutlaq's remarks came a day after the accused lawmaker, Mohammed al-Dayni, claimed to be the victim of a government campaign to silence its critics.

Al-Dayni has frequently spoken out about alleged rights abuses of Sunni prisoners and claims Iran has undue influence over Iraq's Shiite political leaders.

Videotaped confessions by two of al-Dayni's former bodyguards — one of them his nephew — were released last week implicating him as the ringleader of a gang blamed for a string of attacks and abuses, including mortar strikes on Baghdad's Green Zone and a 2007 suicide bombing in the parliament cafeteria that killed one person.

Al-Dayni remains free under parliamentary immunity from prosecution. It was not clear when the parliament would take a vote on whether to strip him of the protection, a move that would clear the way for legal proceedings.

"Let's begin a real effort to disclose information about those involved in killings and sectarian displacement," said al-Mutlaq. "Then we all will discover that there are leaders inside the political process who took part in these events."

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Associated Press writer Sameer N. Yacoub in Baghdad and AP staff in Mosul contributed to this report.