An Al Qaeda in Iraq front group warned Tuesday that insurgents were waiting for the right moment to retaliate against a U.S.-Iraqi security crackdown in the northern city of Mosul.

Gunmen killed a policeman near his station in Mosul, when attackers opened fire with machine guns shortly before noon about 100 yards from the Hadba police directorate, officials said.

Interior Ministry spokesman Maj. Gen. Abdul-Karim Khalaf ordered an immediate investigation and expressed concern that the policeman had been killed in broad daylight Tuesday in an area that was crowded with Iraqi policemen and pedestrians.

Mosul, located 225 miles northwest of Baghdad, has been dubbed by the U.S. military as Al Qaeda's last major urban stronghold in Iraq. The Iraqi government launched an offensive, dubbed Operation Lion's Roar, there earlier this month to clear the area.

Officials have claimed initial success, saying more than 1,200 suspects have been detained, and Iraqi security forces have met little resistance.

But a man claiming to be a spokesman for the Islamic State of Iraq in Ninevah province, which includes Mosul, warned in a videotape posted Tuesday that insurgents were prepared to fight back.

"Until now, we have not been engaged ... because we are the ones who control the hour to start the initiative and we will choose the time for retaliation or engagement," the unidentified spokesman said, sitting with his face covered behind a table with a laptop and wearing a white Arab robe.

"We are at full strength and have not had a single soldier killed or arrested contrary to your alleged reports" of major arrests, he said.

He said that during the first week "of the so-called the Lion's Roar operation" many people from Mosul were arrested, but he claimed they were merely former army officers, university teachers and students.

There was no way to authenticate the comments. But the video was said to have been produced by al-Furqan, one of Al Qaeda's media production wings, and it was posted on a number of Islamic Web sites that usually carry militant statements.

The spokesman also said members of the group would not comply with a government call to hand over weapons, drawing a comparison with similar offensives against Shiite extremists led by anti-U.S. cleric Muqtada al-Sadr's Mahdi Army in the southern city of Basra and Baghdad's Sadr City.

"We tell (Prime Minister Nouri) al-Maliki that the soldiers of the Islamic State of Iraq are not like those from the charlatan Mahdi Army who surrendered their weapons to the soldiers of the crusade for few dollars," he said. "We will not hand over our weapons."

The U.S. military said Sunday that Al Qaeda in Iraq was "off-balance and on the run" after recent operations against it but remains a very lethal threat.

Maj. Gen. Mark Hertling, the top American commander in northern Iraq, also said last week that the military expected the insurgents to try to regroup and strike back against the two-week-old offensive with car bombs and suicide attacks.

The Iraqi military on Monday detained six teenagers it says were trained as suicide bombers by a Saudi militant in Mosul.

Khalaf said the young men, who officials said were ages 14 to 18, would be released after the investigation was completed because they had been forced to comply when the militant threatened their families.

"Due to their ages and the fact that they were coerced and not volunteering, they will not be subject to legal procedures," he said Tuesday.

In other violence, a U.S.-allied fighter was killed and two others were wounded Tuesday when a bomb under their vehicle exploded near a market in northern Baghdad's predominantly Sunni area of Azamiyah.

The attack was reported by a member of a local group that has joined U.S. and Iraqi forces against Al Qaeda in Iraq. He spoke on condition of anonymity because he wasn't authorized to release the information.

The U.S. military also said an American soldier was killed and two others were wounded Sunday afternoon in a roadside bombing 110 miles south of Baghdad near the Ash Shamiyah district of the Qadisiyah province, southeast of the Shiite holy city of Najaf.

On the political front, al-Maliki convened a meeting of the presidential council and other political leaders late Monday to discuss negotiations over a long-term security agreement with the United States that is meant to replace the U.N. mandate that governs American military operations in Iraq.

Nasser al-Ani, a spokesman for the presidential council, said the delegates agreed to continue the dialogue.

"It is not an easy matter but it is a critical one and needs the participation of all influential political parties in the country who have a role in making decisions," he said.

President Bush and al-Maliki signed a statement of principles last December regarding future U.S.-Iraqi relations and said they planned to finalize a new security agreement by July 31.