They have moved between 10-15km (6-16 miles) in the last 24 hours towards the government-held town of Gharian.

The town controls access to one of the main roads leading from the desert northwards towards the capital.

Earlier, rebels in Misrata said progress towards Tripoli was being hampered by a lack of ammunition.

If the rebels can take Gharian, they will control the main north-south road to Tripoli.

But rebel fighters say the town is heavily defended, and they are moving forward carefully to avoid civilian casualties.