Explosions could be heard all over Najaf as US forces launched assaults on several targets around 11:30 pm (1930 GMT).

The intense air raids struck Medina street, which is one of the streets leading to the shrine and flames could be seen shooting into the sky near the golden-domed mausoleum.

Shelling also hit al-Arsood street, which also runs a few yards away from the walls of the mausoleum compound and where militiamen are usually posted.

It was difficult to verify whether the holy site itself had been hit or whether there had been any casualties.

The US military did not immediately comment on the latest operation.

Elsewhere in the city, clashes also broke out between Shiite fighters loyal to Sadr and Iraqi government forces backed by the US-led coalition.

Heavy artillery fire coming from a US base north of the city and targeting the vast Vale of Peace cemetery, where Mehdi Army fighters are dug in, coincided with the intense air raids on the Old City.

The fresh onslaught came after a day of heavy fighting in Najaf, where Sadr's militiamen are still in control of the Imam Ali mausoleum, one of Shiite Islam's holiest shrines.

After more than two weeks of fighting, Sadr's office said Friday the militiamen would leave the mosque compound but disagreements over the modalities of the withdrawal have prevented the proposed handover of the shrine to the Shiite religious leadership.

On Monday, the Iraqi media quoted Najaf police chief Ghaled al-Jazaeri as saying that Moqtada Sadr had left the city, but one of his aides Sheikh Ahmed al-Shaibani insisted the young firebrand cleric was still in Najaf.

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