* Gaddafi forces reported heading for rebel-held border post
* Rebels digging defensive trenches on border with Tunisia
* Gaddafi forces fighting rebels in mountainous region
(Adds rocket fire in Zintan)
By Abdelaziz Boumzar
DEHIBA, Tunisia, April 27 (Reuters) - Libyan rebels who seized control of a remote border post hurriedly dug defensive trenches on Wednesday after hearing that forces loyal to Muammar Gaddafi were on their way to re-take the crossing.
The rebels hoisted their flag over the post last week after government forces melted away from that corner of the Western Mountains region, where pro-Gaddafi forces are trying to stamp out an uprising.
Rebels threw themselves into a frenzy of activity after reports surfaced that government forces were now about 8 km (5 miles) away and heading towards the Dehiba-Wazin crossing.
The sound of distant explosions could occasionally be heard coming from the Libyan side of the border.
At the crossing — in the desert about 100 km from the nearest Tunisian town — rebel fighters were using excavators to dig trenches. On the Tunisian side, the military who patrol the border posted units on nearby hills.
Convoys of lorries carrying fuel crossed into Libya as the rebels rushed to re-supply before the border cut off their lifeline to Tunisia.
“Gaddafi is pretty determined to take back the Wazin checkpoint,” said a Libyan aid worker who has been helping send in supplies to the Western Mountains from Tunisia.
The scenes at the border are the outward sign of a battle that has been going on for weeks in the Western Mountains region, largely out of sight of the outside world.
The area, an arid mountain range running from east to west, is populated largely by Berbers, who speak their own language, are ethnically distinct from most other Libyans and have traditionally been viewed with suspicion by Gaddafi.
Residents say pro-Gaddafi forces have been surrounding mountain-top towns, cutting them off from food, water and fuel supplies and unleashing indiscriminate bombardments on them with rockets and mortars.
Libyan officials deny targeting civilians, saying they are fighting armed gangs and al Qaeda sympathisers who are terrorising the local population.
A rebel spokesman in the Western Mountains town of Zintan, scene of some of the region’s most intense fighting, said there was heavy bombardment there on Wednesday, that at least 15 people were wounded and five houses destroyed.
“Rebels attacked posts belonging to Gaddafi forces east of Zintan in the early evening. The posts have been used to fire rockets into Zintan,” the spokesman, called Abdulrahman, told Reuters. “The rebels destroyed at least three tanks and captured two others.”
He said he heard loud blasts after NATO planes flew over and he believed they had carried out an airstrike nearby.
Tarek Cabawe, a Libyan aid worker inside Tunisia, said Gaddafi’s tanks shelled houses in the town of Yafran and detained around 30 men there on Wednesday. He said Libyan forces had suffered heavy casualties this week near the town of Nalut. (Additional reporting by Hamid Ould Ahmed in Algiers and Joseph Nasr in Berlin; Writing by Christian Lowe; Editing by Matthew Tostevin)