BBC News with Marion Marshall

A new audio message has been broadcast from Colonel Gaddafi, urging Libyans to destroy the rebels as heavy fighting again broke out in parts of Tripoli. He appealed to people in Jfara, a district near Tripoli, to march on the capital and

emulate

the struggle for independence against the former colonial power in Libya, Italy.

"Our tribes in Jfara, march, march, keep marching towards the city of Tripoli as you marched towards Tripoli when it was attacked by the Italians in 1911. The same march is being repeated now.

Confront

them, confront them and

purge

the great city of Tripoli from these rats - the agents of colonialism."

Meanwhile, there's been fighting between rebels and forces loyal to the colonel in the Abu Salim neighbourhood of Tripoli. There have been unconfirmed claims from rebel sources that Colonel Gaddafi or his sons might be hiding in residential buildings in the area.

Rebel forces are now advancing on the city of Sirte, Colonel Gaddafi's birthplace and his

principal

remaining stronghold. A BBC correspondent says the morale of the Libyan rebels is high. He said teenagers sitting on tanks cheered as they passed for what they hope will be the final battle of the war, but our correspondent says the Gaddafi loyalists are

putting up

stubborn resistance. The BBC has been shown evidence of war crimes alleged to have been committed by Colonel Gaddafi's forces just days before the fall of Tripoli. Our correspondent Rupert Wingfield-Hayes has been taken to see the bodies of a group who appeared to have been tortured and shot.