NATO defense ministers were set to meet Thursday to consider options to tackle the ongoing Libya crisis, including imposing a no-fly zone.

While Britain and France are keen on a no-fly zone, the United States and other members of the 28-nation alliance were more cautious.

U.S. Secretary of State Hillary Clinton has stressed that any no-fly zone over Libya must have international backing and not be a Washington-led effort.

Ivo Daalder, the U.S. ambassador to NATO, said a no-fly zone is "not going to be the solution to every problem." He also noted that some members has not made up their minds.

NATO Secretary-General Anders Fogh Rasmussen has insisted that slapping a no-fly zone over Libya would require a very clear international mandate, in particular from the UN.

However, with no such mandate in the cards, the United States, Britain and other countries considering some form of intervention have been seeking alternative support from regional blocs, such as the Arab League, the African Union, and the European Union.

Besides the no-fly zone option, others proposals are also open for discussion on Thursday, including the use of naval vessels to deliver humanitarian aid and to block arms shipments to Libya.

On Wednesday, the NATO chief reiterated his stance that the alliance had no intention of intervening in Libya, but would be ready for all eventualities.