Britain is to send a team of military officers to Libya to help advise the rebels fighting Col Muammar Gaddafi.
The BBC understands about 10 UK officers and a similar number from France will provide logistics and intelligence training in Benghazi.
UK Foreign Secretary William Hague said the move was in accordance with the resolution on Libya, which forbids foreign occupation forces.
The Libyan foreign minister said it would only prolong hostilities.
Abdul Ati al-Obeidi told the BBC the sending of UK military personnel to Libya would harm any peace initiative and "prolong the confrontation".
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Following the fall of presidents in neighbouring Tunisia and Egypt, an uprising against Col Gaddafi's 42-year rule began on 16 February.
It has developed into an armed conflict, with rebels pitted against pro-Gaddafi forces for control over territory. Misrata, the rebels' last stronghold in the west, has faced weeks of heavy bombardment.
The UN Security Council resolution, passed in March, authorised "all necessary measures short of occupation" to protect civilians.
Nato is currently in charge of the no-fly zone and coalition operations have been largely confined to air attacks.
Mr Hague stressed the officers being sent to the eastern rebel stronghold of Benghazi would not be involved in any fighting.
Mr Hague said: "The [UK] National Security Council has decided that we will now move quickly to expand the team already in Benghazi to include an additional military liaison advisory team. This contingent will be drawn from experienced British military officers.
"These additional personnel will enable the UK to build on the work already being undertaken to support and advise the NTC [opposition National Transitional Council] on how to better protect civilians.
"In particular they will advise the NTC on how to improve their military organisational structures, communications and logistics, including how best to distribute humanitarian aid and deliver medical assistance."
The officers will be wearing civilian clothing, not uniforms, but are likely to carry sidearms.
The UK has already supplied body armour and telecommunications equipment to help the rebels.
On Monday it was announced the UK is to provide £2m to help civilians flee Misrata by boat.
Mr Obeidi said countries he had visited had spoken about a ceasefire and helping the humanitarian effort, but pointed to the UK, France and Italy as being unhelpful.
He said everything possible was being done to help international aid organisations give help to people in Misrata.
He said there should be a ceasefire followed by an interim period of maybe six months to prepare for an election, as proposed by the African Union roadmap.
Asked about the future of Col Gaddafi, he said that if that process was followed, "everything will be on the table - it would cover whatever issue is raised by Libyans".
French Foreign Minister Alain Juppe has said France is opposed to the idea of sending coalition ground troops into Libya, or even special forces to guide air strikes, to break the military stalemate.
The UK's shadow foreign secretary, Douglas Alexander, said the move to send UK officers was backed by the UN resolution and Labour supported the government's decision.
Former Liberal Democrat foreign affairs spokesman Sir Menzies Campbell warned against becoming bogged down in Libya, in similar fashion to what happened to the US in Vietnam.
He said: "Sending advisers for a limited purpose is probably within the terms of [United Nations] Resolution 1973, but it must not be seen as a first instalment of further military deployment."
Labour MP David Winnick, who backed last week's demands to recall Parliament from the Easter recess so MPs could debate the Libya situation, criticised the deployment of British officers.
"However much one despises the brutality of the Gaddafi clan which rules Libya, the fact remains that there is a danger of mission creep," he said.
Meanwhile, British military chiefs have been giving details of the latest action by the RAF to enforce the no-fly zone.
Maj Gen John Lorimer said Tornado and Typhoon aircraft had attacked rocket launcher vehicles and light artillery observed firing on Misrata, and a second pair of RAF planes destroyed a gun and tank on a transporter.
Tomahawk cruise missiles were also fired by the nuclear-powered submarine HMS Triumph.
Brig Gen Mark Van Uhm, chief of Allied operations, said almost 2,800 sorties had been flown over Libya, destroying more than a third of Col Gaddafi's military assets.
He said the situation on the ground remained fluid and was changing daily.