NAJAF, Aug 5: At least 16 people were killed on Thursday and a US helicopter was shot down in Najaf in the fiercest fighting between multinational troops and Shia militiamen in Iraq since a truce was brokered in June.

Further north, in Mahawil, at least nine people were killed and more than 20 wounded when gunmen opened fire and a suicide bomber blew up a minibus outside a police station.

In what could be a sign of a fresh coordinated onslaught against occupation troops, Shia leader Moqtada Sadr's representative in Basra declared jihad against British forces after four militiamen were arrested.

Clashes persisted throughout the day in Najaf, and officials reported more than 100 people wounded in the holy city and the Baghdad slum stronghold of Moqtada Sadr. By early evening, US jets began shelling militia positions in Najaf and planes could be heard roaring over the capital.

A US helicopter attached to the Marine Expeditionary unit was forced down in the Najaf region in the morning, a military spokesman in Baghdad said, adding that the crew was recovered alive but the extent of their injuries was unknown.

"A UH-1 marine helicopter was shot down," he confirmed just hours after the fighting started between Iraqi police and Sadr's Mehdi Army militia on Wednesday night. Near Najaf, a US soldier was killed and five were wounded when their convoy was attacked with rocket-propelled grenades and gunfire.

The soldiers had been redeployed to the area from north of Baghdad, the military said. Najaf's general hospital, attacked by rockets in the morning - killing a doctor and seriously wounding four other staff members - said seven people died in the fighting and another 32 were admitted with injuries.

Moqtada Sadr's aides accused US troops of damaging a minaret of the city's holiest shrine, the mausoleum of Hazrat Ali, which has remained a Sadr stronghold since his militia waged an uprising against US forces in the spring.

BASRA: Three militiamen were killed and another three wounded in a brief skirmish with British troops in northern Basra, Sheikh Saad al Basri, Sadr's representative, said.