Updated

Libyan militias in the country's west are vowing to confront a rival army commander's attempt to seize the capital, Tripoli, raising the prospect of renewed civil war.

The advancing forces of Khalifa Hifter, who runs the self-styled Libya National Army based in the country's east, have sparked fears of a major showdown with the militias that control Tripoli.

The militias from the western cities of Zawiya and Misarata posted on social media early on Friday that they're mobilizing to confront Hifter, hours after he ordered his fighters to march on Tripoli.

They posted: "We are the revolutionaries and the elders ... we declare we are on full mobilization and war."

Since the 2011 uprising that ousted and killed Moammar Gadhafi, Libya has slid into chaos and frequent spasms of violence.