Libya: Why is it taking so long?
Rebels holding military positions some 90km (60 miles) from the Libyan capital, Tripoli, have expressed frustration that Nato commanders are holding them back from attacking the approaches to the capital.
"For Nato, the right position is to expedite our move to Tripoli and freedom for us," said Ashour Abu Deir, a young rebel fighter.
"I think Nato is a little way behind because, when we reach Misrata, they say stop, when we reach Bir Ghanem, they say stop, when we reach Brega, they say stop.
"They can do more than this, instead of holding us back," said Mr Abu Deir.
The rebels holding a strategic pocket of territory in the western Nafusa Mountains, or Jebel Nafusa, are in a loose alliance with the opposition Transitional National Council (NTC) with headquarters in Benghazi, eastern Libya.
I reached their easternmost front-lines in the Jebel Nafusa by driving through high, winding roads that thread through rocky terrain.
Their front-line positions are typically mounds of earth, or simple trenches to protect them from incoming fire.
Local commanders say they liaise with Nato through a command centre in Benghazi.
Because Colonel Muammar Gaddafi's forces control most of the heavy weapons, the rebels count on Nato to destroy these before they can move forward more easily on the ground.
Col Gaddafi's heavy artillery - mainly Soviet-era Grad missiles with a range of 30-40km - can pin down a force armed mainly with small machine-guns, typically AK-47 Kalashnikovs.
"Nato doesn't want us to move forward," said a former computer engineer who gave his name only as Muhammad, for fear that his family in Tripoli could be targeted if his full name were known.
"They are afraid of a huge massacre that might happen in Tripoli, by Gaddafi forces because he's using civilians as a shield," he claimed.
Part of this frustration may be born of bluster. Some rebels, highly motivated to advance on Tripoli, do not like to admit the weaknesses of their position.
But others are more circumspect.
"Sometimes Nato is right to be cautious," said Commander Ali al-Hajj, a wiry, energetic man in charge of the rebel front in Yefren, near the easternmost points of rebel control in the Jebel Nafusa.
Cdr Ali al-Hajj could not be accused of any reticence to fight.
I saw him return day after day to a highly dangerous, tenuously-held front line on the edge of the village of Kikla.
He and his men fought fiercely against a better-armed force of Col Gaddafi's troops. His enemies were dug in just a few kilometres away, across a bone-dry, dusty plateau in the crossroads settlement of al-Gwaleesh.
If al-Gwaleesh were controlled by the rebels, it would help open the way to the major town of Gharayan - and the main road from the south to Tripoli.
In just three days of battle for al-Gwaleesh, nine of Cdr Ali's men - who in another life were farmers, engineers and students - were killed, and dozens wounded.
Nato is sometimes cautious "when we are fighting on open ground", Cdr Ali said, because on the flat desert plains "we can be vulnerable".
"In the mountains, it is different", he continued. "We are at home here and can use our shorter-range machine-guns to full advantage."
But behind these rebel theories is an overwhelming reality.
The main reason they cannot advance is, obviously, because Col Gaddafi's forces are stopping them.
The anti-Gaddafi propaganda says he has emasculated Libya's national army.
"It's not a real army any more," said the computer-engineer-turned-rebel Muhammad. "It's just a glorified, bloated bodyguard force for Muammar Gaddafi and his family."
That may be true. But if so, it is a bodyguard force, nevertheless, that has been building up huge stockpiles of weapons and ammunition.
Last week, I visited an arms dump south of the mountain town of Zintan.
I reached it by driving for an hour along the route of an underground oil pipeline laid by the Italian company Agip.
The dump was a large complex of low warehouses squatting in the desert as far as the eye could see.
Nato had destroyed some of them; the rebels were picking over the rest to take away the best of the remaining ammunition.
"This is just huge," I said out loud to myself as I sat in a car overlooking the smouldering remains of the dump. "I've never seen anything like this."
My Libyan companion in the car, a man well-informed about military matters, smiled indulgently.
"Oh, there are plenty more dumps like this," he turned to me to explain. "The colonel has been building up his stocks for years. He has secret supplies all over the country."