(Adds Libya seeking U.N. probe into NATO bombings)
* Gaddafi PM asks for international probe into NATO 'abuses'
* Tunisian army clashes with Libyan fighters
* Oil chief doesn't return in week's 3rd apparent defection
By Tarek Amara and Ulf Laessing
TUNIS/ZAWIYAH, Libya, Aug 20 Libyan rebels
battled for towns on either side of the besieged capital Tripoli
on Saturday, and fighting spilled across the border into Tunisia
where Libyan infiltrators clashed with Tunisian troops.
This week's rebel advances on Tripoli -- Muammar Gaddafi's
last major stronghold -- have transformed the war by cutting the
capital off from its main road link to the outside world and
putting unprecedented pressure on Gaddafi's 41-year rule.
Washington says the veteran leader's days are now numbered,
and reports have emerged of more defections from Gaddafi's
The six-month-old war came close to the Tunisian frontier
after rebels suddenly seized the coastal city of Zawiyah just 50
km (30 miles) west of Tripoli, surrounding the heavily fortified
capital and severing its vital supply routes.
In Tunisia, security sources said their forces had
intercepted Libyan men in vehicles with weapons and fought them
through the night in the desert. They reported several
casualties, but did not say whether the fighters were Libyan
rebels or pro-Gaddafi soldiers cut off from Tripoli.
Residents of the southern Tunisian desert town of Douz told
Reuters by telephone that helicopters were swooping overhead and
troops had been summoned from nearby towns to subdue the
infiltrators, who rode in vehicles without number plates.
The imposition of a siege around Tripoli has trapped its
residents and cut it off from fuel and food supplies. The
International Organisation for Migration said on Friday it would
organise a rescue operation to evacuate thousands of foreign
workers, probably by sea.
Intense fighting continued in Zawiyah, home to an important
oil refinery, on Saturday and rebels occupying the center of the
city said pro-Gaddafi forces showed no sign of retreat.
"Gaddafi will try to take back Zawiyah at any price. He will
keep shelling the hospital," said a rebel fighter as he prepared
for midday prayers in the mosque of Bir Hawisa, a nearby village
where many civilians are sheltering.
"We will not let that happen. We will fight."
East of Tripoli, fighting has been bloodier and rebel
advances far slower. On Friday, opposition forces fought street
battles in the city of Zlitan but suffered heavy casualties, a
Reuters reporter said. A rebel spokesman said 32 rebel fighters
were killed and 150 wounded.
NATO warplanes have hammered Gaddafi military targets since
March under a U.N. mandate to protect civilians. Gaddafi's
government has said the bombs have killed scores of innocent
people, including 27 during a raid on Tripoli this week.
On Saturday, Libyan Prime Minister Al Baghdadi Ali
Al-Mahmoudi spoke to U.N. General Secretary Ban Ki-moon by
telephone requesting an investigation into alleged abuses by
NATO, Libyan state news agency JANA reported.
JANA said Ban had promised to study the proposal.
In another potential blow to Gaddafi, a Tunisian
source said Libya's top oil official, Omran Abukraa, had arrived
in Tunisia after deciding not to return to Tripoli from a trip
If confirmed, it would be the third apparent defection of a
senior Gaddafi associate this week. A senior security official
arrived in Rome on Monday, and rebels said on Friday that
Gaddafi's estranged former deputy Abdel Salam Jalloud had joined
their side in the western mountains.
The siege of Tripoli and the prospect of a battle
for the capital have added urgency to the question of Gaddafi's
fate. The leader has repeatedly vowed never to leave the country
and rebels say they will not stop fighting until he is gone.
A senior U.S. official said on Saturday that the opposition
must prepare to take over power soon. The United States is among
more than 30 nations that have recognised the rebels' National
Transitional Council (NTC) as Libya's legitimate authority.
"It is clear that the situation is moving against
Gaddafi," U.S. assistant Secretary of State Jeffrey Feltman told
a news conference after meeting Libyan rebel leaders at their
headquarters in Libya's eastern city of Benghazi.
"The opposition continues to make substantial gains on the
ground while his forces grow weaker."
(Additional reporting by Missy Ryan in Tripoli and Robert
Birsel in Benghazi, Libya; Souhail Karam in Rabat, Morroco;
Writing by Richard Valdmanis and Peter Graff; Editing by Maria