The UK “must prepare for the long haul” in Libya, Downing Street has said.
Earlier Foreign Secretary William Hague briefed the cabinet about the situation in Libya.
Number 10 said progress was being made in putting greater pressure on Libyan leader Colonel Muammar Gaddafi and there were “grounds for optimism”.
RAF fighter aircraft “successfully attacked” three armoured personnel carriers near the besieged city of Misrata over the weekend.
But a spokeswoman for the prime minister said: “We must prepare for the long haul.”
She said this was not a new policy, simply a broad statement of fact, adding: “It is just sensible planning to enforce United Nations Resolution 1973.”
Earlier, a Nato air strike badly damaged buildings in Col Gaddafi’s compound in Tripoli.
Major General John Lorimer has given an update on the military situation.
He said: “Coalition air patrols have continued to focus on the areas around Misrata, Brega and Ajdabiya, and Yafran.
“On Saturday RAF Tornado and Typhoon aircraft successfully attacked three armoured personnel carriers near Misrata, as well as a surface-to-surface missile facility near the city.
“Eight rocket launcher vehicles were seriously damaged and eight support vehicles are assessed to have been destroyed.”
“RAF aircraft returned to the same missile facility on Sunday and destroyed rocket storage facilities, as well as a main battle tank nearby,” Maj Gen Lorimer added.
“On Monday, UK aircraft engaged a tank near Mizda and a self-propelled gun near Yafran, as well as a number of missile launchers south-west of Misrata.”