Thirteen opposition fighters have been killed near the eastern oil town of Brega where rebels have been pushing to seize the area for nearly a week.

Rebels told Al Jazeera, their position was leaked to Gaddafi's forces by spies within the rebel force.

The opposition controls most of eastern Libya but has not controlled Brega since April. The town has crucial oil and gas supplies and rebels fear that Gaddafi loyalists may sabotage the facilities there if they are forced to retreat.

Al Jazeera's Anita McNaught reports from Brega.