The Foreign Secretary said the case for continuing military strikes remained "utterly compelling" and he dismissed the regime's claims it had ordered a ceasefire as an "utter sham".
Mr Hague told MPs airstrikes were relieving pressure on civilians in Misrata although the hospital was "swamped" with casualties. Ajdabiya continued to be under attack, with reports civilians were being killed by tank shelling.
He said UK forces had so far taken part in 59 aerial missions as well as the air and missile strikes. Last night Britain was involved in a coordinated action against Libyan air defence systems.
Updating MPs in a Commons statement, he said: "The case for this action remains utterly compelling. Appalling violence against Libyan citizens continues to take place, exposing the regime's claims to have ordered a ceasefire to be an utter sham."
Mr Hague said: "Misrata has been under siege for days by regime ground forces, although coalition airstrikes are helping to relieve the pressure on its citizens, many of whom are trapped in their homes without electricity or communications, with dwindling supplies of food and water 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 Qadhafi forces to "massacre" residents in areas under bombardment."
He added: "Our action is saving lives and is protecting hundreds of thousands of civilians in Benghazi and Misrata from the fate that otherwise awaited them. That is what UN Security Council Resolution 1973 was for and that is why we are implementing it."
Turning to Britain's involvement in strikes against the regime, Mr Hague said: "UK forces have undertaken a total of 59 aerial missions over Libya, in addition to air and missile strikes.
"Last night, our forces again participated in a co-ordinated strike against Libyan air defence systems.
"A no-fly zone has now been established and the regime's integrated air defence system has been comprehensively degraded. There are no Libyan military aircraft flying.
"Over 150 coalition planes have been involved in military operations, including Typhoon and Tornado aircraft from the Royal Air Force.
"Thirteen nations have currently deployed aircraft to the region. A number of additional nations have made offers of aircraft and other military support, which are in the process of being agreed.
"Royal Navy vessels are in the region supporting the arms embargo."
The Foreign Secretary told MPs that he wanted to see operations moved from the command of the United States to Nato "as quickly as possible".
"We need agreement to unified command and control for it to be robust, and we expect to get that soon," he said.
He added: "Resolution 1973 lays out very clear conditions that must be met, including an immediate ceasefire, a halt to all attacks on civilians and full humanitarian access to those in need.
"We will continue our efforts until these conditions are fulfilled. The Libyan regime will be judged by its actions, not its words.
"Our message to the Gaddafi regime is that the international community will not stand by and watch them kill civilians, a view this House overwhelming endorsed last week.
"To his forces, we say that if they continue to take part in Gaddafi's war against his own people, they will continue to face the military force of the coalition, and if they commit crimes against Libyan people, they will be held to account."
Mr Hague told MPs the Government continued to engage in "intensive diplomatic activity" to keep up international pressure on the regime.
"Further UN and EU sanctions had been agreed including EU designation of the National Oil Corporation of Libya, which would cut off oil revenues."
He added: "We are gravely concerned for the well-being of up to 80,000 internally displaced persons.
"The Secretary of State for International Development is in close communication with his counterparts in international organisations about immediate and longer-term humanitarian support to the Libyan people."
Mr Hague went on: "It is not for us to choose the government of Libya - that is for the Libyan people themselves.
"But they have a far greater chance of making that choice now than seemed likely on Saturday, when the opposition forces were on the verge of defeat and the lives of so many were in danger."
Shadow foreign secretary Douglas Alexander said Labour supported the operation but would "scrutinise the Government's actions in implementing the mission".
He said it should retain "broad international and regional support" and welcomed the London conference on Libya next week.
He asked about reports that mercenaries were still arriving in Libya and what action was being taken against countries that provided such mercenaries.
"Do you believe a lead individual of international standing should now be appointed to take charge of coordinating post-conflict planning?" he asked.
"The House and the public will want to know what work is under way on contingency planning."
Mr Alexander also urged the Government to keep MPs regularly informed on the mission, including the potential recall of Parliament during the Easter recess.
On command and control, Mr Hague said: "The simplest and most effective solution is for all of these operations that are being conducted within Nato to come under the North Atlantic Council, and for other countries then to plug into that, to work with that.
"We have made a great deal of progress and I think we should understand that this is a new coalition put together very quickly, for obvious reasons, last week.
"So there are bound to be issues to sort out in its management but we are getting through those pretty well.
"I will be discussing the remaining issues with Secretary Clinton and with my French and Turkish counterparts later this afternoon to try to iron out the remaining difficulties on future Nato command and control."
Turning to reports of mercenaries entering Libya, he said: "Given the danger they may pose to civilians, they do so at their peril and they should be aware of that."
Mr Hague said the Government would make further statements as necessary, adding: "We will do whatever is necessary to keep the House informed."
Richard Ottoway, Conservative chairman of the Commons Foreign Affairs Select Committee, asked about the arms embargo and whether it meant rebels could be supplied with weapons.
"Is there any way in which support, in some form or another, can be given to the rebels who are facing a fairly unequal battle at the moment?"
Mr Hague told him: "We continue to review the position on that."
There were a "variety of legal opinions" but "whatever we do on that and on all the issues involved, we must be in strict accordance with the United Nations resolution and retain the legal and moral and international authority that comes from that".
He added: "We will not do anything that we think would transgress on that resolution, we are looking at it in that light.
"I will update the House when we have come to any conclusion about that."
Mr Ottoway's Labour predecessor as the committee's chairman, Mike Gapes, asked about the African Union's role in reacing a peace settlement.
Mr Hague said: "There is a role, although of course the peaceful resolution of this does require the Gaddafi regime to observe resolution 1973."
Former Liberal Democrat leader Sir Menzies Campbell asked about the military command structure, saying the current arrangements were "not sustainable in the long term" but any transition must be "both effective and smooth".
Mr Hague said discussions about control of the mission have "in no way impaired" the military operation.
He would raise the issue with US secretary of state Hillary Clinton later and "there is common determination among all the nations involved to sort this out".
