At least three international oil companies have halted production in Libya, which pumps nearly 2 percent of world output. Some companies have been pulling employees and their families out of Africa's third-largest producer, though others say they are keeping oil flowing there.

Oil prices surged as much as 6 percent on Monday, taking Brent crude in London to almost $109 a barrel at one point for the first time since 2008. Prices remained strong on Tuesday, but closer to $106.