UK Apache attack helicopters have been used over Libya for the first time, Nato has confirmed.
They attacked and destroyed two military installations, a radar site and an armed checkpoint near Brega, the Captain of HMS Ocean told the BBC.
The Apaches are understood to have faced incoming fire.
Meanwhile, it has been confirmed that Foreign Secretary William Hague has arrived in rebel-held Benghazi in eastern Libya.
He is due to hold talks with the head of Libya's opposition National Transitional Council (NTC), Mustafa Abdul Jalil, later.
International Development Secretary Andrew Mitchell has also made the trip to Benghazi.
French Gazelle helicopters also took part in simultaneous attacks on different targets in Libya for the first time.
On Wednesday, Nato extended its mission in Libya by 90 days.
Major General Nick Pope, the chief of the defence staff's strategic communications officer, said:"The Apaches were tasked with precision strikes against a regime radar installation and a military checkpoint, both located around Brega.
"Hellfire missiles and 30mm cannon were used to destroy the targets. The helicopters then returned safely to HMS Ocean."
He said the targets had been "carefully and rigorously selected" and said intelligence about the positions of the Gaddafi forces had been improving "despite their efforts to conceal themselves".
Defence Secretary Liam Fox added: "The attack helicopter is yet another potent and formidable aircraft type which has now been added to the Nato forces engaged on this operation. Those who are still supporting Colonel Gaddafi would do well to realise that the best way to remove themselves from danger is to understand that their future lies with the Libyan people, not a discredited regime."
The former head of the Army, Lord Dannatt, said the move has an "inevitable intensification".
"If you pick up the words from when President Obama was visiting, what we've heard the prime minister say, we don't want to let this thing linger on any more than we absolutely have to.
"The mission under UNHCR 1973 is quite clear, it's to protect people but of course the implied task, and let's be absolutely open and honest about it, is the removal of Colonel Gaddafi."
The decision to send four British Apache helicopters to Libya was made by Prime Minister David Cameron on 27 May.
Their deployment via HMS Ocean means there should be less chance of civilian casualties in operations that previously relied on the use of Tornado and Typhoon aircraft.
But the Apaches operate at lower altitudes and could be targeted by Libyan forces loyal to Col Gaddafi, which still have access to thousands of surface-to-air missiles.
Labour MP Graham Allen claimed the introduction of Apaches was "mission creep" and said there needed to be a fresh debate in the House of Commons on Libya.
"The way out of this mess is not to keep cranking up the military hardware and having so-called 'implied tasks' added on against the express view of the House of Commons; what we need to do is figure out how we can get a political solution that will last for several generations in Libya rather than this adventure which has no prospect of coming to a close," he said.
Nato intervened in Libya after the UN passed a resolution for the protection of civilians, amid a two-month revolt inspired by other uprisings in the Arab world.
It has intensified raids in recent weeks with attacks on command-and-control structures in the capital Tripoli.
The intervention was initially led by France, Britain and the US until 31 March - when Nato took over. It was given an initial 90 days, which would have run out on 27 June.
On Wednesday, UN investigators accused government forces in Libya of war crimes and crimes against humanity.
Rights experts said they had found evidence of crimes including murder and torture, in a pattern suggesting Libyan leader Muammar Gaddafi was behind them.
The UN mission also said opposition forces were guilty of abuses that would constitute war crimes, although they were not so numerous.