David Cameron has insisted there is no prospect of British forces becoming part of an "occupying army" in Libya.
Amid concerns that the deployment of UK military personnel as advisers to the rebels is a sign of mission creep, the Prime Minister said: "We're not allowed, rightly, to have an invading army, or an occupying army."
Speaking to BBC Scotland radio, he added: "That's not what we want, that's not what the Libyans want, that's not what the world wants."
MPs have expressed alarm at the announcement that British forces were being sent to Libya to act in an advisory capacity to opponents of Colonel Muammar Gaddafi.
Defence Secretary Liam Fox compounded concerns about a drawn-out engagement by saying the UK's role in Libya is "not that different" to that in Afghanistan in terms of training up local forces.
As Nato sought to intensify pressure on the Gaddafi regime, the US announced that President Barack Obama had authorised the use of unmanned Predator drone aircraft in Libya.
American Defence Secretary Robert Gates said the commitment was indicative of the kind of capabilities the US could contribute to allied efforts to enforce the United Nations-approved no-fly zone.
The deployment of drones - which had been scheduled to start today but was postponed because of bad weather - will allow low-level precision attacks on forces loyal to Gaddafi.
The announcement came ahead of an expected visit to Washington by Dr Fox and General Sir David Richards, the head of the Armed Forces, who are understood to be hoping for greater air support from the Americans.
Earlier, Ministry of Defence spokesman Major General John Lorimer said Nato jets had fired on targets in both the western city of Misrata, which is under siege from Gaddafi's troops, and the capital Tripoli.
"Given the grievous situation in Misrata, Nato has focused much of its air effort in this area, attacking numerous regime targets that were threatening the civilian population," he said.
Baroness Amos, the former Labour minister and now Under-Secretary General for Humanitarian Affairs at the United Nations, cautioned that sending military advisers risked blurring the allies' role.
"We have to be extremely careful about that and make sure the lines are not blurred," she said.
Lady Amos vetoed a plan for the deployment of up to 1,000 EU troops to secure aid missions which has been drawn up by senior officials including Lady Ashton, another Labour peer, who is the EU's foreign policy chief.
Meanwhile, the Libyan government ramped up its rhetoric against Nato, warning that "it will be hell" for the alliance if it sends in ground troops.
Yesterday, it was reported that Libyan rebels seized control of a border post on the Tunisian border from about 100 government soldiers.
Fierce fighting also continued in the besieged, rebel-held western city of Misrata, which has been the target of prolonged bombardment from Gaddafi's forces.
Seven people were reported to have been killed, bringing the total to 20 for the past three-days,
Residents have said they are being targeted by snipers firing indiscriminately and also said they have remnants of cluster bombs.
The Libyan government has so far denied the charge.Reuse content