Libya's rebels tried to push Muammar Gaddafi's army westward out of firing range of the oil town of Brega on Tuesday, as mines and the remnants of the strongman's army slowed their progress.

Some 30 kilometres (19 miles) west of Ajdabiya and around double that distance east of Brega, the rebels' rear artillery was still being fired, a day after they claimed they had control of the town.

Fighters said it was in response to an attack from the desert earlier in day. A rebel position 15 kilometres from Brega had been hit by Grad rockets, killing many, they said.

Rebel colonel Ahmed Omar Bani said a Gaddafi spy had phoned in the coordinates of the position via satellite phone. The suspect had been arrested, he said.

While the alleged spy was being questioned the rebels responded: a row of four giant barrels thumped shells westward over the heads of the rebel positions, hoping to thwart further attack.

At least seven rebel fighters were killed and 45 wounded during the day, medics said. It was not clear how many were killed in the Grad attack.

At the front, rebel forces continued to try to push Gaddafi loyalists westward out of range of the rebel holding positions east of Brega, and from Brega itself.

Rebel military sources said some Gaddafi forces were still thought to be at Bishr to the west, and were arcing rockets over Brega down onto rebel positions.

Maghri Faraj, 25, said his tank unit had spent the morning on Brega's outskirts -- firing on Gaddafi positions beyond the other side of the town -- when he was hit.

"We came up from the south. We saw no sign of Gaddafi troops inside Brega," he said.

"We were firing beyond Brega. We fired and fired with no response, and then one rocket came in and knocked me off the tank. The next thing I know I'm in the hospital."

Rebel officials said the bulk of rebel forces were still waiting to enter the city, hampered by vast quantities of mines and trenches filled with flammable liquids.

Abdulrazag Elaradi, a National Transitional Council (NTC) member from Tripoli who was visiting the front, said that in one 7.5 kilometre tract the rebels had found more than 700 mines.

"This has never been done before, people have to know about this," he said, appalled that Gaddafi would mine his own country.

One soldier accompanying a wounded comrade to Ajdabiya hospital showed an AFP correspondent a picture on his camera that appeared to show a vast roadside trench full of petrol.

The trench was not ablaze, but he said others were, forcing the rebels to be cautious.

The rebels were also trying to get the remnants of Gaddafi's troops in the town to surrender.

"The elite troops have withdrawn, they have left. The soldiers left in the city are stuck," said the NTC's Elaradi.

"They cannot go forward because they will be killed by the rebels and they cannot go back because they will be killed by Gaddafi's men."

An NTC spokesman on Monday said an estimated 150-200 Gaddafi troops were still in the town. That figure could not be independently verified.

While trying to secure their hold of Brega, the rebels said their aim was now to take out Gaddafi artillery posts and to establish forward positions at Uqayla, west of Brega.

They hope the sand dunes and marsh that envelope the village will provide an easily defensible front line for the next stage of their campaign.