A Libyan rebel fires into the air after the capture of the Dhuheiba border crossing between Libya and Tunisia. (Photo: AP Photo/APTN)

TRIPOLI, Libya (AP) — Libyan forces in more than a dozen military vehicles and armed with anti-aircraft guns and rocket launchers crossed into Tunisia on Friday as fighting with rebels raged along the western frontier, witnesses said. Tunisia's government was furious after clashes broke out on its territory and demanded Libya halt all incursions.

In another sign that Moammar Gadhafi's regime was redoubling efforts to beat back resistance in its stronghold of western Libya, NATO warships intercepted several boats laying anti-shipping mines outside the harbor of the rebel-held city of Misrata. The port is the only lifeline for the city of 300,000, which has been under siege by Gadhafi's forces for two months.

Libyan forces also fired rockets and shells at Misrata from the outskirts of town, killing at least eight people.

The fighting on the Libyan-Tunisian border, the attempted mining of the waters near Misrata and the renewed shelling signaled a new push by Gadhafi's forces to retake the two areas of fiercest rebel resistance in the west. It's unlikely Gadhafi would be able to cling to power without consolidating control over western Libya.

The rebels have largely controlled the eastern part of the country since an uprising against Gadhafi, Libya's ruler of 42 years, erupted in mid-February. They have said they will not contemplate a cease-fire before he is pushed out.

The Dhuheiba border crossing between Libya and Tunisia has been a flashpoint in recent days. The crossing has been changing hands repeatedly between regime forces and rebels, who retook it Friday.

The crossing is key supply line for Libya's Nafusa mountain area, near Tunisia, from where members of Libya's ethnic Berber minority have been fighting Gadhafi's forces.

On Friday, there were different accounts of what exactly happened in the Tunisian border town of Dhuheiba, about three miles (five kilometers) from the border. Witnesses aid more than a dozen Libyan military vehicles, carrying troops armed with anti-aircraft guns and rocket launchers, drove into town, setting off clashes. Three Tunisians were hurt.

Ismail al-Wafi, a Dhuheiba resident, said the Libyan forces fired indiscriminately. He said Dhuheiba residents clashed with the Libyans and Tunisian troops eventually captured some and took their weapons.

Another witness said Libyan troops clashed with Libyan rebels in Dhuheiba before they were defeated by Tunisian troops. Some of the Libyans were captured and the others chased out, said the witness, who only gave his first name, Akram, for fear of reprisals. "Gadhafi forces are no longer in Dhuheiba. They were defeated," he said.

The Tunisian news agency TAP said Tunisian forces fired in the air, but did not clash with Libyan troops.

Dhuheiba resident Mohamed Hedia said angry Dhuheiba civilians and the families of Libyan rebels who had been staying there set upon the Gadhafi troops, creating a "chaotic situation." Tunisian forces fired warning shots, Hedia said.

It was unclear why the Libyans entered Dhuheiba in the first place.

One witness said they were fleeing from rebels who had recaptured the border crossing earlier Friday. An Associated Press Television News crew saw two bodies of Libyan troops near the crossing Friday. The crew was told rebels were chasing two dozen Libyan military vehicles on the Libyan side in hopes of securing a supply corridor to the mountain area.

The Nafusa mountain range is home to Berbers who have complained of systematic discrimination by the Libyan government. Thousands of Libyans from the mountain communities have fled to Dhuheiba and other Tunisian border towns in recent weeks, as rebels and government forces battled for control of the border crossing.

On Thursday, Libyan troops briefly recaptured the crossing from the rebels, and some of the fighting spilled over into Tunisia, witnesses said. Mongi Slim, a representative of the Tunisian Red Crescent in the area, said at least two people were killed and 20 wounded Thursday, all Libyan troops.

Late Thursday, the Tunisian Foreign Ministry issued an angry statement.

"Given the gravity of what has happened ... the Tunisian authorities have informed the Libyans of their extreme indignation and demand measures to put an immediate stop to these violations," the statement said.

On the Misrata front, the mining of the waters "shows his (Gadhafi's) complete disregard for international law and his willingness to attack humanitarian deliver efforts," said British Brig. Rob Weighill, director of NATO operations in Libya.

Though rebels have managed to expel regime forces from the city itself, the enclave is isolated and remains dependent for much of its food and other supplies on the sea link with the rebel capital of Benghazi.

It appeared to be the first time sea mines have been used in the Libyan conflict. Weighill said NATO crews were disposing of the mines.

In Misrata, loud booms resonated through the city as regime loyalists fired shells and mortars.

Gadhafi forces fired with tanks and anti-aircraft guns on a group of 50 rebel fighters in the village of Zawiyat al-Mahjoub, on the outskirts of the city, said rebel fighter Abdullah Shiguman, 31.

Medics scrambled to evacuate six bodies and 10 wounded people to the hospital. Some of the wounded had lost limbs and huge chunks of flesh. One was a medic who had been shot in the back. Two of the dead were carried in bundled in blankets holding nothing more than body parts. Earlier, two people had been killed in the shelling.

Rebel field commander Salahidin Badi said Gadhafi's force had been firing mortars and rockets into the city all morning and that rebels had fired back with mortars. Badi said a shoe factory had caught fire during the battle.

"There are lots of materials and fuel there, so if anything blows up there, it will catch fire," he said.

Meanwhile, a NATO spokeswoman said rebel chief of staff Abdel-Fatah Younes met Thursday with senior NATO officials in Brussels. Carmen Romero said there had been "an exchange of views on Libya," but declined to elaborate.

Younes, a former Libyan interior minister who defected to the opposition, called on the international community to supply heavy weapons to the rebels.

It has been a month since NATO assumed control of the U.S.-led military operation in Libya, with the mandate to protect civilians from attack. Since then, alliance warplanes have conducted a total of 4,242 sorties and 1,766 strike sorties. In addition, a total of 19 NATO ships are patrolling the central Mediterranean.

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Associated Press writers Ben Hubbard in Misrata, Libya, Slobodan Lekic in Brussels, Bouazza Ben Bouazza in Tunis, Tunisia and Angela Charlton in Paris contributed reporting.