Fears of militia violence and calls for a boycott threatened today to mar Libya’s first nationwide parliamentary election.

Explosions and heavy gunfire were reported in the Libyan capital Tripoli as rebel forces claimed they had launched an offensive against Muammar Gaddafi's forces in coordination with Nato.

Libyan rebels have fought their way into the strategic city of Zawiya west of Tripoli on in their most significant advance in months, battling snipers on rooftops and heavy shelling from Muammar Gaddafi’s forces holding the city.

The head of the Libyan rebel armed forces was shot and killed just before arriving for questioning by rebel authorities, their political leader said in a carefully worded statement to reporters that gave few details on who was behind the killing.