UPDATE 3-NATO-led air strike kills 13 Libyan rebels
* Rebels say bombing a mistake, call for more air strikes
* Gaddafi forces repulse rebels beyond Brega
* Aircraft heard overhead, rebels speak of stalemate
(Adds updated air strike death toll)
By Alexander Dziadosz
BREGA, Libya, April 2 (Reuters) - A NATO-led air strike killed 13 Libyan rebel fighters as they tried to take control of Brega, before forces loyal to Muammar Gaddafi pushed them back beyond the oil town's eastern limits on Saturday.
The rebel leadership described the deaths as an unfortunate mistake and called for continued air strikes against Gaddafi's forces, who thrust east from Brega with rockets and machineguns.
The rapid advance sent hundreds of anti-government fighters fleeing down the coast road, erasing two days of rebel gains.
Better-trained and experienced rebel fighters had earlier been fighting Gaddafi's forces inside Brega, but it was unclear whether they held their ground or pulled back into the desert. Journalists moved back east with the rebels.
Earlier a Reuters correspondent saw at least four burnt-out vehicles including an ambulance by the side of the road near the entrance to Brega.
Men prayed at freshly dug graves covered by the rebel red, black and green flag nearby.
"Some of Gaddafi's forces sneaked in among the rebels and fired anti-aircraft guns in the air," said rebel fighter Mustafa Ali Omar. "After that the NATO forces came and bombed them."
Rebel fighters at the scene said the bombing happened around 10 p.m. local time (2000 GMT) on Friday.
Most blamed a Gaddafi agent for drawing the "friendly fire" but some said other rebels had shot into the air by accident.
"The rebels shot up in the air and the alliance came and bombed them. We are the ones who made the mistake," said one fighter who did not give his name.
Thirteen died in the bombing and seven were injured, rebel national council spokesman Hafiz Ghoga said in the eastern city of Benghazi, calling it a "regrettable incident".
Another rebel spokesman, Mustafa Gheriani, said: "You have to look at the big picture. Mistakes will happen. We are trying to get rid of Gaddafi and there will be casualties, although of course it does not make us happy".
He said the rebel leadership still backed air strikes to protect Libyan civilians. "We are pleased to see the NATO forces doing what they are assigned to do -- protecting civilians, enforcing a ceasefire and creating a situation to allow peaceful protests," said Gheriani.
REBELS WAIT EAST OF BREGA
Without the air strikes the rebels, most of whom lack basic military training, have been unable to hold territory against Gaddafi's better-armed troops.
Their commanders have tried to hold lighter-armed volunteers back until better-trained fighters from army units that renounced Gaddafi secure territory at the front.
The rebels moved heavier weapons and a top commander to the front line near Brega on Friday.
Later a Reuters television reporter filmed more than 20 bodies of what appeared to be Gaddafi soldiers near Brega's university.
But the rebel advance appeared to fizzle out on Saturday morning and the Gaddafi forces used heavy weapons to push them beyond the eastern approach to the oil town.
By mid-afternoon, dozens of volunteer fighters were waiting with their pick-ups at a checkpoint close to the positions they held two days earlier.
Volunteer fighter Khalid Salah said the rebels were waiting for the arrival of heavy weapons to begin another counter-attack. Aircraft could be heard occasionally overhead.
"When they (the Gaddafi forces) hear the sound of aircraft, they get scared and don't move," said Salah.
Some rebels were scouting around the desert in trucks. "Gaddafi placed troops on top of hills and we are afraid of flanking," said rebel fighter Mustafa Meriami.
Fear that Gaddafi was using spies to infiltrate and undermine the rebels added to the tension. The rebels stopped a man driving east out of Brega and dragged him from his car when they saw he was wearing a watch bearing Gaddafi's face.
"He had a watch with Muammar's face on it at time like this?" said one rebel.
The rebels said the man was a spy for Gaddafi's revolutionary committees and packed him into a car. One said he was being sent to Benghazi for questioning. (Additional reporting by Angus MacSwan, Writing by Tom Pfeiffer; editing by David Stamp)