FORMER Liberal Democrat leader Sir Menzies Campbell has claimed Libya could turn into another Vietnam unless the government proceeds with caution in offering military help.
• Rebel fighters walk past a car destroyed by what they say was a NATO air strike, in the western gate of Ajdabiyah earlier this month
While Mr Hague insisted they would not be involved in combat training or fighting but would provide logistical support for humanitarian aid and communications, the move was seen by many critics of the conflict as the latest evidence of "mission creep".
Sir Menzies 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.
"Vietnam began with an American president sending military advisers. We must proceed with caution."
Mr Hague insisted the use of advisers was within the UN mandate to defend the civilian population and said it did not amount to mission creep.
He said army officers would help prevent attacks on civilians, in line with the UN Security Council resolution authorising military action against Gaddafi's forces.
He went on: "These additional personnel will enable the UK to build on the work already being undertaken to support and advise the (rebel] 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.
"Our officers will not be involved in training or arming the opposition's fighting forces. Nor will they be involved in the planning or execution of the NTC's military operations or in the provision of any other form of operational military advice."
The increase in Britain's commitment brought criticism from MPs across the Commons, with fresh demands for a recall of parliament.
Some right-wing Tories are unhappy with Britain taking sides in a civil war, and the MP Peter Bone said parliament, currently on a break, should be recalled to debate the issue.
"We are now looking at regime change, and we are clearly backing the rebels. We seem to be taking sides in a civil war," he said.
"That may well be right, but it's not for the government to decide - it's for parliament to decide."
Fellow Conservative MP John Baron said: "The mission in Libya has changed quite significantly. When it was put before the House, the emphasis was very much on humanitarian assistance. This has changed into a mission of regime change."
They were backed by a veteran left-wing Labour MP David Winnick, who said: "However much one despises the brutality of the Gaddafi clan which rules Libya, the fact remains that there is a danger of mission creep.
"There is a civil war in Libya and this is a big escalation of Britain's involvement. I don't think there is an appetite in Britain for military intervention.
"Having been engaged in two wars in nine years in Muslim countries, it would be unwise to become involved in a third."
Britain's move is likely to anger Russia, which has already said that western attempts to topple Gaddafi violate the UN resolution.
"The UN Security Council never aimed to topple the Libyan regime," Russian foreign minister Sergei Lavrov said in Belgrade.
"All those who are currently using the UN resolution for that aim are violating the UN mandate."
Meanwhile, the head of the foreign affairs commission in France's lower house has proposed sending 200 to 300 special non-combat forces to help designate targets for Nato planes, but foreign minister Alain Juppe said yesterday he was "totally hostile" to the deployment of ground troops.
He told journalists rebel forces "can play this role without it being necessary to deploy troops on the ground".
However, the sense of a step-up in military operations by the allies appeared to be confirmed when the European Union made clear it was ready to send in an armed force - Britain would not be involved.
The force is ready to be sent to Libya to ensure delivery of humanitarian aid.
But the move by the EU to deploy armed units to escort humanitarian aid drew an immediate warning from the Gaddafi regime that this would be tantamount to a military operation.
There are increasing concerns among European leaders about the consequences of the conflict in Libya, with a tide of immigrants fleeing across the Mediterranean to Italy.
Yesterday, a boat carrying 760 people, most of them from sub-Saharan Africa, arrived on the southern Italian island of Lampedusa from Libya. The boatload was one of the largest to arrive in years on the tiny island, located roughly midway between Sicily and Tunisia, which has been at the centre of an immigration crisis triggered by the upheavals in North Africa.
On the ground in Libya, Misrata, the country's third-largest city with a population of 300,000, has been under siege for nearly two months, with rebels holding on to seaside positions in the port area. In recent days, Libyan troops have pounded the city with shells and rockets. Yesterday, rebels and troops clashed again in central Misrata, and explosions and gunfire were heard.
Britain, meanwhile, revealed details of its latest attacks on military targets by the RAF and Tomahawk missiles fired from submarine HMS Triumph.
Nato officials have acknowledged they are having trouble destroying Gaddafi's mortars and rocket launchers from the air, for fear of inadvertently harming civilians in such strikes - although the fact is that not enough aircraft are available to provide proper cover.
The fighting in Libya has been deadlocked for the past month. Gaddafi is holding on in the west, while the rebels control the east. Nato air strikes have kept Gaddafi loyalists in check, but the rebels, a poorly trained group with little military experience, have not been able to score military gains either.
The UN World Food Programme said it had, with Libyan consent, sent eight trucks from Tunisia with 240 tonnes of food - enough to last 50,000 people for 30 days - to towns in the west, including Zawiyah, Zintan and Nalut that are mostly under Gaddafi's control after uprisings were crushed.