BAGHDAD, Iraq - Coalition troops battled militiamen loyal to Shiite cleric Muqtada al-Sadr in several Iraqi cities today, the second day of fighting that has shattered truces to end a widespread rebellion two months ago.

Some of the worst clashes occurred in the Baghdad neighborhood of Sadr City, where the Health Ministry said 19 people were killed and 111 wounded during fighting Thursday and early today between U.S. troops and al-Sadr militants. Separate attacks blamed on al-Sadr's followers wounded 15 American soldiers in Baghdad.

The fighting began Thursday in the holy city of Najaf and has since spread to other areas across the country, and dozens have been reported killed and wounded. Also today, members of al-Sadr's Mahdi Army militia seized four police stations in Amarah, 180 miles southeast of Baghdad, witnesses said.

Helicopter gunships pounded militant positions in fierce fighting in Najaf, while Italian soldiers exchanged gunfire with militants who attacked their positions and a police station in the southern city of Nasiriyah, an Italian military spokesman said. Clashes were also reported today between U.S. troops and insurgents north of the capital in Samarra.

Each side blamed the other for breaking the ceasefire. The U.S. military accused the militants of repeatedly attacking police in Najaf, and al-Sadr loyalists accused U.S. forces of surrounding the cleric's house on Monday.

In Najaf, 100 miles south of Baghdad, U.S. helicopters today attacked militants hiding in a cemetery near the Imam Ali Shrine in the old city at Najaf's center, where smoke could be seen rising.

Gunfire and explosions rang out as U.S. soldiers and Iraqi policemen advanced toward the area, witnesses said. The streets were otherwise deserted and shops were closed.

The U.S. military has accused the militants of hiding in the shrine compound to avoid retaliation by U.S. forces.

In Samarra, 60 miles north of the capital, guerrillas attacked a convoy of 10 U.S. Humvees at dawn, witnesses said. U.S. helicopters fired rockets at insurgent positions, and the U.S. convoy pulled out.