BAGHDAD, Iraq - U.S. troops killed 18 insurgents after coming under attack in the volatile city of Ramadi, the military said Friday.

The fighting began Thursday night when insurgents opened fire on the Americans from several positions in the city, 70 miles west of Baghdad, the military said.

The U.S. forces returned fire with machine guns and a missile, which struck the intended target, the military said, adding that at least 15 insurgents were killed in that attack.

Insurgents armed with rocket-propelled grenades and small arms renewed attacks against U.S. forces on Friday, the military said, prompting another missile to be launched that killed at least three insurgents.

No civilian or U.S. casualties were reported in either attack, the military said.

Ramadi, the capital of the western province of Anbar, has seen some of the bloodiest street battles of the war. Sunni insurgents remain well-entrenched in the city and continue to move freely through parts of downtown where Americans often dare not set foot.