Planning for NATO's no-fly operation over Libya assumes it will last three months but it could be more or less, a NATO official said on Friday, while coalition air forces continued to hit Muammar Gaddafi's forces.
The UN-mandated no-fly mission, approved by NATO states on Thursday, will involve dozens of planes from the 28-nation military alliance and is expected to start early next week.
NATO spokeswoman Oana Lungescu said the alliance would decide in the coming days whether to broaden its role to take command of ground strikes to protect civilians, a mission now being conducted by a coalition led by France, the United States and Britain.
In the meantime, she said, "the coalition operation will continue to put pressure on the Libyan regime".
Asked about the timeframe for the no-fly mission, the NATO official said: "Much of the planning assumptions were based on a three-month planning window, but should the (NATO commander) feel it's necessary to extend it, then he would simply have to say... I am anticipating it may be more or less".
A military briefer said the aim of the mission was to close Libyan air space to all but authorised aid flights and it would bar flights both by Libyan leader Muammar Gaddafi's forces and his opponents.
"No-fly zones are impartial -- there is no one authorised to fly in that area," Group Captain Geoffrey Booth said.
NATO officials said the mission was expected to involve 5-10 AWACS surveillance planes, 10-15 refuelling tankers, as well as a dozens of fighters.
About 10 NATO countries and the Gulf state of Qatar have pledged aircraft and apart from commonly funded NATO assets, costs of the mission will be borne by contributing states.
Booth said the mission would be run from NATO's Joint Operations Command centre at Naples in Italy. It will be under the command of U.S. Admiral Samuel Locklear, the operations commander of the coalition mission, but rules of engagement for the NATO mission will be clearly delineated, Booth said.
"If they are directly targeted, crews can act in self-defence," he said. A response to a perceived threat, rather than direct targeting, would have to come via the chain of command with the principle being to "always apply the minimum force required to achieve effect", he said.
NATO pilots would be able allowed to engage ground targets, such as surface-to-air missiles, but only if threatened.
"You have right to respond," he said. "It doesn't give you the right to just bomb targets on the ground."
Booth said his understanding was that the threat posed by Gaddafi's air defences had been "significantly degraded".
The decision for NATO to take over the no-fly zone from the coalition was held up by French concerns about the unpopularity of the US-led alliance in the Arab world and Turkey's desire to limit operations against Libyan infrastructure and to avoid casualties among Muslim civilians.
NATO officials said a decision was expected on Sunday on whether to broaden the mandate to take full command of military operations, including over attacks on ground targets to protect civilian areas under threat from Gaddafi's forces.
France has wanted to see the operation put under a broader political umbrella to include Arab states.
NATO officials said if all 28 member states agreed to expand the role of the alliance, it would give it political control of military operations.
However, they said it would "take into account" the guidance of a high-level political platform to include Arab states expected to be established at a conference in London on Tuesday.