Libyan rebels said their steady advance on Brega was slowed Saturday by the discovery of defensive trenches around the city that had been filled with flammable chemicals by retreating Kadhafi troops.

After a small rebel reconnaissance force from the north punched through to Brega late on Friday before falling back, a rebel commander said troops were now moving "slowly but surely" toward the town from the east and south as well.

"We are advancing and we are very close to Brega," said Mustafa al-Sagezli, a member of the rebel's revolutionary military council, adding that strongman Moamer Kadhafi's troops had fallen back to positions inside the town.

But the commander said landmines and a series of booby-trapped trenches had forced them to slow the attack in order to minimise casualties.

"We know Kadhafi's forces have installed a lot of mines. They have even dug holes and trenches (filled) with some chemical liquids and oil to fire them when our forces enter Brega," he said.

It was not clear what kind of chemicals were being used, but the oil hub is home to a large petrochemical facility that produces a range of oil by-products.

Libya's largely volunteer rebel army began their push on Brega late on Thursday, hoping to oust an estimated 3,000 loyalist fighters and provide a moral boost for war-weary rebel supporters.

By Saturday morning the rebels' forward position to the north was four kilometres from the town centre, while a second unit attacking from due east of Brega faced stiffer resistance and was about 10-20 kilometres (six to 12 miles) from the town.

"Most of Kadhafi's troops seem to be at the centre," said rebel military spokesman Mohammed Zawi.

But the assault took its toll, with at least 10 dead and 172 wounded, according to medics.

At a hospital in Ajdabiya where most of the wounded were brought, Doctor Ahmed Dinari said many of the casualties were now caused by landmines rather than Kadhafi's heavy artillery, as earlier on in the offensive.

"We have had five more injuries this morning, all of them from mine explosions," he said.

Lying prone in "Bed 2," 19-year-old Ali Saleh said he had been in the central rebel column in the early hours of the morning when his armoured personnel carrier hit a mine.

"We were very close to Brega at around three in the morning. Then we got instructions from NATO to fall back and as we were falling back the vehicle hit a mine, destroying the chain track."

He was suffering from shock and a lightly damaged knee.

Commander El-Sagezli said 250 mines had been uncovered so far.

To the south of the town, where the rebels had made initial gains but suffered large numbers of casualties, Kadhafi forces had pushed back harder wounding many rebels with rocket fire.

But the rebels got much needed assistance from NATO overnight.

The alliance said on Friday it hit one tank, a multiple rocket launcher, five armoured vehicles and seven armed vehicles around the town.

Meanwhile in raids near the Libyan capital Tripoli, NATO aircraft took out a radar facility and a surface-to-air missile launcher.

And southwest of the capital, a rebel checkpoint commander Shaban Aaboz said Kadhafi troops had fired five missiles at their forces who responded with rockets.

"There has been no fighting in the valley (near to Gualish); it is quiet. Kadhafi's forces have carried out several operations but they are sufficiently far from us not to pose any problems," he added.

Gualish has changed hands several time, the latest being on Wednesday when Kadhafi forces briefly seized most of it back, only to be driven out later towards Asabah.

Another commander said rebel forces were still positioned near Asabah, 80 kilometres (50 miles) south of Tripoli and the last obstacle between rebels and the garrison town of Gharyan.

"The position is secure; we are discussing with Asabah people how civilians can get out of town before we launch an assault," said commander Mokhtar Lakhdar.

Rebels were buoyed on Friday by the news that in Istanbul the Contact Group recognised the rebels' National Transitional Council as "the legitimate governing authority in Libya" until an interim government is formed.

A defiant Kadhafi called the Contact Group's recognition of the rebels "insignificant." He said he could not imagine the day "the heroic Libyan people would be represented by a fistful of traitors who opened the doors of Benghazi to crusaders."

burs-arb/al