Libyan leader Muammar Gaddafi is "on the back foot", Defence Secretary Liam Fox has said, citing new momentum in Nato's air campaign.
He said there had been "significant progress" in the past 72 hours against Col Gaddafi's forces in Misrata.
He was speaking at a press conference at the Pentagon after meeting US Defence Secretary Robert Gates.
Foreign Secretary William Hague has said "diplomatic, economic and military pressure" will be stepped up on Libya.
Nato is enforcing a UN resolution to protect civilians in Libya amid a two-month revolt inspired by other uprisings in the Arab world.
But the city of Misrata in the west of the country continues to come under attack by Libyan government forces attempting to retake it. Three people were reportedly killed on Tuesday as missiles slammed into the city's port, a lifeline for those seeking to escape to the rebel stronghold Benghazi.
Speaking before the latest bombardment, Mr Fox said: "We have seen significant progress made in the last 72 hours with Gaddafi's forces losing their grip on Misrata and we have received reports of under-age soldiers and foreign mercenaries being captured - this underlines the regimes inability to rely on its own security forces.
"These are the tactics of an increasingly desperate and weak regime."
He said of the international community's enforcement of the UN resolution: "We understand our duty and our resolve will not waver as long as that civilian population remains at risk from an aggressive and wicked regime which has waged war on its own people."
Asked about a Nato air strike on Monday on Col Gaddafi's compound in Libya, Mr Gates told reporters that command and control centres were "legitimate" targets, although Nato was not targeting Col Gaddafi specifically.
Mr Fox added: "All that we want is that men, women and children can sleep safe in their own homes knowing that they will not be attacked by their own government."
UK Chief of the Defence Staff General Sir David Richards discussed the situation in Libya with his US counterpart Admiral Mike Mullen, chairman of the joint chiefs of staff.
Last week, Adm Mullen said the war in Libya was "moving towards stalemate" despite the destruction of 30-40% of Col Gaddafi's ground forces.
Mr Hague rejected suggestions Nato - and the US in particular - was not deploying its full military capability in Libya, saying the US was responsible for a quarter of all missions and more aircraft were being made available by Italy and other nations.
"Time is not on Gaddafi's side because the diplomlatic, economic and military pressure on him will only intensify in the coming weeks," he told BBC Radio 4's Today programme.
Asked again whether Col Gaddafi was a specific target for coalition forces, Mr Hague added: "People are targets depending on the way they behave. It depends on their behaviour not on who they are. It depends whether providing all necessary measures to protect civilians in Libya requires them to be a target."
The UK has so far given £13m of aid to Libya, including food for 10,000 people in Misrata.
Labour has said it supports the increased assistance being given by the UK to the rebel fighters, including the provision of body armour and communications equipment.
But it said the manner in which the move was announced - during the parliamentary recess which ended on Tuesday - was "unco-ordinated" and there was "no clearly articulated plan" behind the step.