Libya says gunmen believed to be former rebels have kidnapped Prime Minister Ali Zeidan and taken him to an unknown location.
The government said in a statement Mr. Zeidan was taken "for unknown reasons" early Thursday from a Tripoli hotel where he lives.
A group of former rebels known as the Operations Room of Libya's Revolutionaries claimed responsibility, saying they "arrested" the prime minister.
The group had blamed Mr. Zeidan's government for playing a role in Saturday's U.S. special forces raid in Libya that nabbed senior al-Qaida operative Abu Anas al-Libi, who is being held aboard a Navy ship.
Libya called on the United States to explain the operation, which it termed a "kidnapping." Mr. Zeidan said Tuesday his country wants to keep good relations with the United States, but that Libyan citizens should be judged at home.
U.S. Secretary of State John Kerry defended the capture, calling it "legal and appropriate." He said the Libyan government's complaints are unfounded, and that Libi will go before a court of law.
U.S. State Department spokeswoman Jen Psaki, who is traveling with Kerry, said Thursday the U.S. is looking into the prime minister's abduction and is in close touch with Libyan officials.
British Foreign Secretary William Hague condemned the abduction and called for the prime minister's immediate release. He also stressed the need for Libya to maintain its political transition process.
Libya has struggled with instability and violence since the ouster of longtime dictator Moammar Gadhafi in late 2011.
Rebel groups that fought against Mr. Gadhafi's forces have given rise to militias and militant groups who control parts of the country.
Attacks have targeted foreign diplomatic missions in Libya, including the Russian embassy last week, the French embassy in April and a U.S. consulate last year.