The fighters’ advance five days ago to the outskirts of the small town of Bir Al-Ghanam had raised the possibility of a breakthrough in a four-month old conflict that has become the bloodiest of the Arab Spring uprisings.

Opposition fighters who had been massing on a ridge near Bir Al-Ghanam and preparing for an attack were now pulling back under fire from Russian-made Grad rockets, said a Reuters photographer in Bir-Ayyad, 30 km to the south.

He said the rocket barrage was now reaching as far back as Bir-Ayyad, a road junction in the foothills of the Western Mountains range southwest of Tripoli from where the fighters had launched their advance last week.

The reversal underlines the resilience of Qaddafi’s forces, who have withstood 15 weeks of bombardment by NATO missiles and warplanes, and attempts by opposition fighters on three fronts to break through their lines.

Frustration at the slow progress is growing inside the military alliance, with some members worried about the cost, civilian casualties and the fact the campaign has now been going on much longer than its backers anticipated.

There are also differences about how proactive NATO members should be in aiding the rebels, who are hampered by a lack of organization and a shortage of equipment.

France this week became the first member of the anti-Qaddafi alliance to acknowledge that it had supplied weapons to the opposition fighters, saying this was justified to protect civilians under threat from Qaddafi’s forces.

It said it used parachutes to drop assault rifles and rocket launchers, along with humanitarian supplies, to fighters in the Western mountains.

That admission prompted Russia, a permanent member of the United Nations Security Council, to accuse France of a “gross violation” of a UN arms embargo.

Even France’s NATO allies distanced themselves from the French operation, though Britain and the United States said they believed it was justified under UN rules.

Libyan state television reported that NATO had bombed military and civilian sites in the government-controlled town of Garyan, on the eastern edge of the Western Mountains.

NATO said it had successfully destroyed a military target in the town on Friday.

“It should be noted that the target was well outside the built-up area of the conurbation and no collateral damage was observed afterwards. At no time was any civilian area targeted,” a NATO official said.

Qaddafi has said the NATO campaign is an act of colonial aggression aimed at stealing Libya’s plentiful oil. His aides say arrest warrants issued on Monday by the International Criminal Court for him, his son and his brother-in-law have no legitimacy because the court is a tool of the West.