Libyan prime minister Ali Zeidan has been seized by armed men from a hotel in the capital, Tripoli.
Mr Zeidan was taken at dawn "by gunmen to an unknown place for unknown reasons", a statement on the Government's website said.
The BBC reports sources saying Mr Zeidan was arrested by an anti-crime department militia, but others that he had been kidnapped.
On Tuesday he called on the West to help stop militancy in Libya.
In an interview with the BBC on Monday, Mr Zeidan had said Libya was being used as a base to export weapons throughout the region.
Last month Mr Zeidan visited Britain and appealed for help to remove weapons from the country amid fears of increased arms smuggling to Syria.