NATO has promised "all necessary resources" to Libya's opposition in its campaign to topple Muammar Gaddafi, but the military alliance continues to disagree on whether that includes arming rebel fighters.

The pledge, made by Anders Fogh Rasmussen, NATO's secretary general, came during a two-day meeting in Berlin marked by disputes over how to resolve the Libyan conflict and the extent of the alliance's support for the rebels.

Rasmussen added that NATO would maintain "a high operational tempo against legitimate targets" in its mission to enforce a UN-approved no-fly zone over Libya.

Libyan rebels have criticised NATO, which took command of operations over the country on March 31, for not doing enough to prevent attacks on rebel-held towns and cities by forces loyal to Gaddafi, Libya's long-term leader.

"People have been quite upset since NATO took over the command because they thought that NATO has been extremely slow in its air strikes," said Al Jazeera's Hoda Abdel-Hamid, reporting from the rebel stronghold of Benghazi.

Opposition supporters blamed NATO for reverses which have pushed the rebels back towards the east of the country and allowed Gaddafi forces to lay siege to the western city of Misurata, our correspondent said.