Islamic State militants in Libya seized a group of foreigners at the al-Ghani oilfield last week, a spokesman for the Austrian foreign ministry said citing "secure information" on Monday, adding that they were alive when taken.

There has been no sign since of the nine oil workers from Austria, the Czech republic, Bangladesh, the Philippines and at least one African country who went missing, the spokesman said.

"We know that they were not injured when they were transported away from the al-Ghani oilfield," the spokesman said, adding Austria had information the group was taken by Islamic State militants.

Foreigners have increasingly become targets in Libya's turmoil, where two rival governments are battling for control and Islamist extremists have grown in the chaos that followed Muammar Gaddafi's ouster four years ago.