Forces loyal to Libyan leader Muammar Gaddafi launched a new armoured incursion into the besieged rebel city Misurata yesterday as his son, killed in a Nato-led air strike, was buried in Tripoli.

AFP correspondents heard heavy shelling throughout the morning as loyalist tanks thrust into the western suburbs of Libya’s third largest city.

At least four people were killed and some 30 wounded in the fighting, medical sources said. Clashes overnight had killed another six and wounded dozens more.

“The tanks are in Al-Ghiran and Zawiyat Al-Mahjub and have been halted by our men,” a rebel commander said.

AFP correspondents heard one or more Nato aircraft overflying the city for more than two hours, but no air strikes were heard.

Residents expressed exasperation at the lack of a military response from the Western alliance to Colonel Gaddafi’s armour.

“Nato has to help us. What are they waiting for?” asked one.

Unlike on previous days of the more than six-week-long siege of Misurata, the resident declined to give his name – an indication of the mounting fear in the city that Col Gaddafi’s forces are poised to retake it.

The last major rebel bastion in western Libya, Misurata is surrounded by pro-Gaddafi forces and entirely dependent on supply by sea.

Nato forces were searching for a loose anti-ship mine laid by Gaddafi forces near Misurata last week, the alliance said on yesterday. Four small boats were caught dropping three mines off the port on Friday, but only two were found and disarmed, a Nato statement in Brussels said.

“Two were moored to the seabed and were later destroyed, but a third mine drifted free before specialised ships could arrive,” it said.

Late yesterday, Misurata was again targeted by rockets and shells, an AFP reporter said, and heavy explosions were heard in the port area.

In the capital, more than 1,000 people attended the funerals of Col Gaddafi’s second youngest son.

Regime spokesman Mussa Ibrahim told reporters early on Sunday that Seif al-Arab was killed in the air strike on a Tripoli compound, along with three of the leader’s grand­children.

They were a boy and a girl, both aged two, and a baby girl of four months.

The official Jana news agency had said that their funerals were also being held yesterday, but no children’s bodies could be seen.