UK forces have launched further missiles at Libyan air defences during a fifth night of coalition action to enforce a UN-backed no-fly zone. Eleven countries are taking part in the action to protect Libyan civilians.
Foreign Secretary William Hague told MPs the case for it remained "utterly compelling".
In a statement to the Commons, he said: "Appalling violence against Libyan citizens continues to take place, exposing the regime's claims to have ordered a ceasefire to be an utter sham.
"Misrata has been under siege for days by regime ground forces, although coalition air strikes are helping to relieve the pressure on its citizens.
"Many... are trapped in their homes... and facing sniper fire if they venture into the streets, while the local hospital is swamped with casualties.
"Ajdabiya continues to be under attack, with reports of civilian deaths from tank shells.
"This underlines the appalling danger its inhabitants would be in without coalition action, as do continued threats by Gadaffi forces to 'massacre' residents in areas under bombardment."
On Wednesday the RAF commander of the air operations, Air Vice Marshal Greg Bagwell, said the Libyan air force was no longer a fighting force.
Ships from Nato nations have also started patrolling off the Libyan coast to enforce a UN arms embargo against Col Muammar Gaddafi's regime.
They aim to intercept and board ships suspected of ferrying arms to the Libyan government.
'Watching over innocent'
AVM Bagwell said the coalition was now applying pressure on Libya's armed forces.The chief of defence staff's strategic communication officer, Maj Gen John Lorimer, said the missiles launched on Wednesday night were part of the coalition plan to enforce the UN resolution.
"Britain and her international partners remain engaged in operations to support United Nations Security Resolution 1973, to enforce the established no-fly zone and to ready the UK's contribution to the Nato arms embargo of Libya," he said.
AVM Bagwell, speaking during a visit to RAF aircrew based at Gioia del Colle, in southern Italy, said: "We are watching over the innocent people of Libya and ensuring that we protect them from attack.
"We have the Libyan ground forces under constant observation and we attack them whenever they threaten civilians or attack population centres."
Speaking in the Commons on Wednesday, Prime Minister David Cameron told MPs that 11 nations were contributing more than 150 aircraft.
He confirmed that Qatari Mirage jets had been taking part in the operation, and said there would be "logistic help" from countries like Kuwait and Jordan.
'Good effect'
The prime minister said the coalition operation over Libya had had a "good effect" in protecting civilians, but that it was still early days.The foreign secretary has announced that the UK will host an international conference on Libya next week.
The coalition action began after the United Nations Security Council authorised the use of military force in Libya in order to protect its citizens from attacks by Col Gaddafi's regime.
Security Council Resolution 1973 called for a ceasefire and the imposition of a no-fly zone over Libya, and it imposed a freeze on "all funds, other financial assets and economic resources" owned or controlled by the Libyan authorities.
Many in the rebel-held cities in eastern Libya have welcomed the intervention, with thousands marching on Wednesday to show their gratitude for the no-fly zone.
