France and Italy have said they are to send small teams of military officers to advise Libyan rebels who are seeking to topple Col Muammar Gaddafi.
French officials said fewer than 10 would be sent, while Italy's defence minister announced that 10 would go.The UK said on Tuesday it was sending a similar team to the city of Benghazi.
Meanwhile, the UN has said the reported use of cluster munitions by Col Gaddafi's forces in the city of Misrata "could amount to international crimes".
"Reportedly one cluster bomb exploded just a few hundred metres from Misrata hospital, and other reports suggest at least two medical clinics have been hit by mortars or sniper fire," UN High Commissioner for Human Rights Navi Pillay said in a statement.
Ms Pillay said the deliberate targeting of medical facilities was a war crime, and the deliberate targeting or reckless endangerment of civilians might also amount to serious violations of international humanitarian law.
"I urge the Libyan authorities to face the reality that they are digging themselves and the Libyan population deeper and deeper into the quagmire. They must halt the siege of Misrata," Ms Pillay added.
She also urged Nato forces to exercise the utmost caution and vigilance so as not to kill civilians by mistake. French President Nicolas Sarkozy has promised to intensify air strikes.
US officials meanwhile told the Associated Press that the Obama administration had decided to give the rebels $25m (£15.2m) in "non-lethal assistance" after assessing their capabilities and intentions.
Inspired by uprisings in neighbouring Tunisia and Egypt, the rebels have been fighting Col Gaddafi's forces since February. The rebels, based in Benghazi, hold much of the east, while Col Gaddafi's forces remain in control of Tripoli and most of the west.
On Wednesday, Libyan state television reported that Nato aircraft were bombarding telecoms and broadcasting infrastructure in several cities.
French government spokesman Francois Baroin reaffirmed that France had no intention of sending a military force to Libya, saying: "We do not envisage deploying combat ground troops."
However, Defence Minister Gerard Longuet said the idea of such a deployment was "a real issue" that deserved consideration by the UN Security Council.
The BBC's Hugh Schofield in Paris says that in France, as in Britain, there is concern about the Libyan campaign turning into an open-ended commitment as both governments push to its limits the UN resolution endorsing the protection of civilians in Libya.
The comments came as the chairman of the Libyan rebel Transitional National Council, Mustafa Abdul Jalil, met French President Nicolas Sarkozy in Paris, where he thanked the French "for their brave decision to support the Libyan revolution".
Mr Sarkozy said the rebels had promised to build democracy in Libya "by the ballot box, not atop a tank". He also pledged to "intensify the strikes", an aide said, although no further details were given.
Announcing that his country would also send military advisers, Italian Defence Minister Ignazio La Russa said: "There is a clear understanding that the rebels have to be trained."
He also said stronger intervention within the terms of UN Security Council resolution 1973 - which authorises "all necessary measures short of occupation" - might be needed.
The British team, which like the French and Italian teams is expected to comprise about 10 advisers, will provide logistics and intelligence training in Benghazi. UK Foreign Secretary William Hague said it complied with the UN mandate.
'Mountain towns bombarded'
On Tuesday, Libyan Foreign Minister Abdul Ati al-Obeidi told the BBC that the presence of foreign military personnel would be a "step backwards".
He proposed that there should be a ceasefire followed by an interim period of maybe six months to discuss democracy and constitutional reforms, and prepare for an election that would be supervised by the UN, as proposed by the African Union.
Misrata, Libya's third largest city, has faced weeks of heavy bombardment. Hundreds of people have been killed.
Fighting was continuing on Wednesday in the centre, with rebels telling the Reuters news agency that they had made some gains. Eight people were killed on Tuesday, most of them civilians, they added.
The Libyan government says it is trying to protect the citizens of Misrata and to help international aid organisations provide aid there. It also denies shelling densely-populated areas.
"We welcome any objective investigation of the actions of our army, our government and our officials," said spokesman Moussa Ibrahim.
Rebels in the western Nafusa region told the Associated Press that the town of Yifran had been under attack with rockets, shells and anti-aircraft guns since the weekend. Clashes were also reported in Qalaa and Nalut.