* Cameron says Gaddafi will be judged by actions not words
* UK sends Tornadoes and Typhoons for no fly zone operation
* Cameron: statement to come on what Gaddafi must do next
(updates with response to Libyan ceasefire announcement)
By Matt Falloon and Adrian Croft
LONDON, March 18 (Reuters) - British Prime Minister David Cameron gave a cautious reaction to a ceasefire declaration from Libya on Friday, saying its leader Muammar Gaddafi would be judged by actions not words.
Cameron had earlier told parliament Britain was starting to move fighter jets to bases from where they can help enforce a no fly zone over Libya.
Gaddafi's government then said it was halting military operations after the United Nations passed a resolution authorising military action against it. "We will judge him by his actions not his words," Cameron told BBC TV.
"What is absolutely clear is the U.N. Security Council resolution said he must stop what he is doing, brutalising his people. If not, all necessary measures can follow to make him stop.
"That is what we agreed last night, that is what we are preparing for and we'll judge him by what he does."
Speaking earlier to parliament, Cameron said the international community would soon set out what it expected from Gaddafi.
"The clock is now ticking and we need now a sense of urgency because we do not want to see a bloodbath in Benghazi and further repression and killing of civilian life in Libya," Cameron told parliament.
Gaddafi had vowed to crush rebels who are fighting to dislodge him from power and the UN authorised military attacks on the Libyan leader's forces to protect civilians.
Gaddafi, who has been condemned across the world for the brutality of his crackdown on the uprising, had also warned residents of dissident stronghold Benghazi in eastern Libya that his troops would show no mercy.
Cameron said it was right that the latest U.N. resolution excluded any invasion force on Libyan territory, but emphasised there was "a clear and unequivocal legal basis for the deployment of UK forces and military assets".
"This is not about an army of occupation," Cameron said.
Instead, Britain, still divided over protracted and controversial military campaigns in Afghanistan and Iraq, would send fighter jets as part of an international effort.
"Britain will deploy Tornadoes and Typhoons as well as air-to-air refuelling and surveillance aircraft," Cameron said.
"Preparations to deploy these aircraft have already started and in the coming hours they will move to airbases from where they can start to take the necessary action."
Critics of last year's defence review -- part of Britain's efforts to slay a record budget deficit -- had warned that Britain might struggle to participate in any military intervention in Libya.
The prime minister will attend a summit in Paris on Saturday to discuss the situation with French President Nicolas Sarkozy and Arab leaders. (Additional reporting by Keith Weir; editing by Philippa Fletcher)
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