TRIPOLI, Libya — The ousted prime minister fled Libya to Europe after parliament voted him out, leaving behind a country that risks being torn apart as the fault line between its eastern and western regions broke open Wednesday to a degree unseen since the 2011 civil war that usurped longtime strongman Moammar Gadhafi.

A western-based militia fighting in the name of parliament has launched an offensive against an autonomy-minded militia in the east that has for months occupied most of Libya’s crucial oil facilities – seizing virtual control of the country’s most vital resource and almost sole source of cash. This past week, it succeeded in exporting a tanker of oil from a port it holds in defiance of the central government.

In response to the offensive other militias in the east are rallying to fight back. Eastern leaders have warned that unless Tripoli backs down they will seek independence for their region rather than greater autonomy.

Since Gadhafi’s fall, Libya has been torn among multiple, rival, heavily armed militias affiliated to regions, cities and tribes, while the central government has been weak, unable to bring its authority over the country, inheriting Gadhafi-era military and police forces thrown in disarray. Furthermore, militias have lined up on rival sides of a political struggle between Islamist politicians and their opponents.

Now the success by the Islamist-leaning parliament in voting out secular figure Ali Zidan as prime minister on Tuesday has sparked fears among their opponents of a power grab by the Islamists – tensions that also could translate into militia clashes.