Several strong explosions have shaken Tripoli early Tuesday as NATO warplanes repeatedly bombed targets around the Libyan capital.
Correspondents on the scene describe it as one of the most intense series of airstrikes since NATO's air campaign against the forces of Libyan leader Moammar Gadhafi began. More than a dozen explosions were heard in the first hour of the raids.
A government spokesman reported casualties, but that could not be confirmed.
Britain and France have decided to deploy attack helicopters to join the NATO air campaign. French Foreign Minister Alain Juppe Monday said the deployment falls within the United Nations mandate to protect Libyan civilians. He said it will take place as soon as possible.
NATO has about 200 aircraft at its disposal for the operations in Libya, but it has not used any helicopters to conduct its core mission of hitting Gadhafi forces threatening civilians.
A high-ranking U.S. diplomat is on a three-day visit to the Libyan rebel stronghold of Benghazi in what the State Department calls "another signal" of America's support for the rebels' Transitional National Council. Assistant Secretary of State for Near Eastern Affairs Jeffrey Feltman is the most senior U.S. official to visit Libya since the uprising against Moammar Gadhafi began in February.
A State Department statement called the NTC "a legitimate and credible interlocutor for the Libyan people."
On Sunday, the European Union's foreign policy chief, Catherine Ashton, opened an EU office in Benghazi.
Some information for this report was provided by AFP and AP.