AL ARBAEEN (Libya) - Libyan rebels regained ground in a new advance on an oil port on Wednesday but accused NATO of inaction hindering their quest to oust Muammar Gaddafi. NATO said Gaddafi was making it increasingly difficult for its pilots to carry out air strikes by ensconcing his forces in heavily populated areas and using civilians as human shields. In their eastern heartland, ill-trained insurgents thrust back westwards toward the contested oil port of Brega, recovering mostly desert terrain lost in a pell-mell retreat from Gaddafi's superior firepower the day before. Rebels returning to the tiny outpost of al-Arbaeen, midway between Brega and their frontline town of Ajdabiyah, spoke of rocket duels close to Brega's port as both sides strived to end a ragged stalemate in the oil-producing state's civil war. There was little doubt the rebels had made ground after falling back at least 40 km (25 miles) on Tuesday but it was impossible to verify accounts that they were closing in on Brega once again. There were reports of mortar and rocket battles near the town on Libya's desolate Mediterranean highway 80 km (50 miles) west of Ajdabiyah. Fighting had resumed at daybreak after government forces were resupplied with ammunition and swung east from Brega, rebel officer Mohamed el-Masrafy told Reuters. "God willing, we are going to try to enter Brega today," said rebel Idriss Abdel Karim, but he and various comrades complained of a lack of support from NATO bombers. "(Government forces) are scared of NATO air strikes but NATO doesn't bomb anything in the first place," he said. "There have been no air strikes. We hear the sound, but they don't bomb anything," said Hossam Ahmed, another rebel. "What is NATO waiting for? We have cities that are being destroyed. Ras Lanuf, Bin Jawad, Brega, and Gaddafi is destroying Misrata completely," added Said Emburak, an Ajdabiyah resident. NATO's air strikes are targeting Gaddafi's military infrastructure but only to protect civilians, not to provide close air support for rebels, much to their dismay, as part of a no-fly zone mandated by the U.N. Security Council.