Libya's internationally recognised government called for outside help against military advances in the country by the Islamic State jihadist group and warned of an Iraq-like scenario.

"Libyan cities are coming under increased threat from this group and it will become difficult to confront them, like in Iraq," Prime Minister Abdallah Thani told a press conference on Sunday in Al-Baida in eastern Libya where his administration is based.

In remarks quoted on the government's official Facebook page, Thani said: "We are surprised that the international community has not taken a firm stand on what is taking place in Libya."

Thani renewed demands for a lifting of the international arms embargo, in place since Libya's 2011 NATO-backed uprising which toppled longtime dictator Moamer Kadhafi, to defeat the IS jihadists, whose counterparts have seized control of swathes of Iraq and Syria.

IS took control of the airport in Sirte, Kadhafi's hometown east of Tripoli, after forces belonging to a Tripoli-based rival government withdrew last week.

Officials in Tripoli said IS had allied with supporters of the ousted Kadhafi regime to deploy across Sirte, which lies in a region rich in oil fields.

The Tripoli administration has also called for international help to combat IS, which has exploited the chaos in Libya since the 2011 revolution to make territorial gains.