Colonel Muammar Gaddafi's air force "no longer exists as a fighting force", the commander of British aircraft operating over Libya has said.
Air Vice Marshal Greg Bagwell said the allies could now operate "with near impunity" over the skies of Libya.
He said they were now applying unrelenting pressure on the Libyan armed forces.
Latest reports say government tanks are shelling the hospital in the rebel-held western city of Misrata.
Witnesses had earlier said the tanks encircling the city had pulled back from their positions under air assault from international forces.
And there are also reports of fierce fighting between rebels and pro-Gaddafi forces in the strategic eastern town of Ajdabiya. Residents fleeing the town described shelling, gunfire and houses on fire.
Wednesday night also saw reports of a huge explosion at a military base in the Tajura region 32km (20 miles) east of the Libyan capital Tripoli.
US Secretary of State Hillary Clinton has again urged Col Gaddafi to step down and leave Libya.
UN Secretary General Ban Ki-moon has urged all sides in Libya to cease hostilities. "All those who violate international humanitarian and human rights law will be held fully accountable," his spokesman Martin Nesirky said.
AVM Bagwell was speaking during a visit to RAF aircrew based at Gioia del Colle in southern Italy.
"We are watching over the innocent people of Libya and ensuring that we protect them from attack," he said.
"We have the Libyan ground forces under constant observation and we attack them whenever they threaten civilians or attack population centres."
His comments come as Nato members debate who should lead the intervention, with the US keen to hand over to Nato.
They were echoed by Rear Admiral Gerard Hueber, US chief of staff for the Libya mission, who said: "We are putting pressure on Gaddafi's ground forces that are threatening cities." Asked if that meant air strikes, he replied: "Yes."
Speaking to reporters by phone from the command ship USS Mount Whitney, in the Mediterranean, he insisted there had been no reports of civilian casualties caused by allied action.
"Our mission here is to protect the civilian populace and we choose our targets and plan our actions with that as a top priority."
He said allied aircraft had flown 175 sorties in the last 24 hours - 113 of them by US aircraft.
Meanwhile, ships from Nato nations have started patrolling off the Libyan coast to enforce a UN arms embargo against Col Gaddafi's regime.
A spokesman for the Western military alliance, Canadian Brig Gen Pierre St Amand, said six vessels were taking part in the first day of patrols.
They aim to intercept and board ships suspected of ferrying arms to the Libyan government.
"If, after inspection, doubts remain as to the legitimacy of the cargo, the vessel will be diverted to a designated port for further inspection," said Gen St Amand.
Nato members have been holding talks about assuming responsibility for the no-fly zone over Libya, so far without agreement.
Turkey is an integral part of the naval blockade but expressed concern about the alliance taking over command of the no-fly zone from the US.
US Defence Secretary Robert Gates has arrived in the Egyptian capital Cairo for talks on both Libya and Egypt's hoped-for transition to democracy following the fall of Hosni Mubarak.
He was previously in Moscow, where President Dmitry Medvedev criticised what he called the "indiscriminate use of force" by coalition aircraft in Libya.
Mr Gates rejected the criticism of the air strikes, saying Col Gaddafi was lying about civilian casualties.
Russia abstained from last week's UN Security Council resolution that authorised armed intervention in Libya to protect civilians.