An al-Qaida in Iraq front group warned on Tuesday that insurgents were waiting for the right moment to retaliate against a US-Iraqi security crackdown in the northern city. Gunmen killed a policeman near his station in Mosul, when attackers opened fire with machine guns shortly before noon about 100 meters from the Hadba police directorate, officials said. Interior Ministry spokesman Maj. Gen. Abdul-Karim Khalaf expressed concern that the policeman was killed in broad daylight Tuesday in an area that was crowded with Iraqi policemen and pedestrians. He ordered an immediate investigation. Mosul, 360 kilometers (225 miles) northwest of Baghdad, has been dubbed by the US military as al-Qaida's last major urban stronghold in Iraq, and the Iraqi government launched an offensive, dubbed Operation Lion's Roar, 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 with little resistance.