The US military has confirmed the first strike by an unmanned Predator drone aircraft in Libya.
Nato said the drone destroyed a Libyan government multiple rocket launcher near Misrata at approximately 1100GMT.
Drones can hit military targets more easily in urban areas, minimising the risk of civilian casualties.
Earlier, Libya's government warned that tribes loyal to Col Muammar Gaddafi might take over the fight against the rebels in the western city of Misrata.
The deputy foreign minister said the Libyan army was being withdrawn and suggested that the tribes would not show the same level of restraint over civilian casualties.
But a rebel military spokesman in Benghazi said Col Gaddafi was "playing games" and would not allow his forces to leave Misrata.
Human rights groups say more than 1,000 people have died there.
Several hours after the Pentagon's announcement confirming the Predator strike, Nato revealed that the target had been a "Gaddafi regime multiple rocket launcher (MRL) in the vicinity of Misrata".
"The MRL system had been used against civilians in Misrata," the alliance said in a statement.
Predators have previously been used in Libya only for intelligence, surveillance and reconnaissance missions.
On Thursday, Defence Secretary Robert Gates said President Barack Obama had approved air strikes in support of the Nato-led mission because that was where the US had "some unique capabilities".
Gen James Cartwright, the vice-chairman of the US Joint Chiefs of Staff, said forces loyal to Col Gaddafi were digging in or "nestling up against crowded areas" to avoid being targeted by Nato warplanes.
The more precise Predators bring "their ability to get down lower and therefore, to be able to get better visibility, particularly on targets that have started to dig themselves into defensive positions," he added.
The BBC's Peter Biles in Benghazi says the first drone attack in Libya could mark the start of a new phase of Nato's air campaign.
It is certainly a further attempt to protect civilians who are under attack from Libyan government forces, our correspondent adds.
Early on Saturday, two missiles apparently fired by Nato aircraft struck a concrete bunker near Col Gaddafi's Bab al-Aziziya compound in Tripoli.
Government spokesman Moussa Ibrahim said three people were killed by a "very powerful explosion" inside a water storage facility.
However, journalists who were taken to the site reported that it seemed like the bunker was being used for military activities. Smoke was rising from one of the two craters and ammunition crates lay nearby.
'Misinformation' in Misrata
Meanwhile, fierce clashes are continuing between rebels and government troops on the outskirts of Misrata, Libya's third largest city.
On Friday, the rebels said they had driven Col Gaddafi's forces from buildings along Tripoli Street, from where snipers had been shooting at anyone who ventured out including women and children.
Libya's Deputy Foreign Minister, Khaled Kaim, said the army might stop fighting in Misrata and withdraw because of the threat of further Nato air strikes.
He said local tribes would instead try to negotiate with the rebels, and if that failed, the tribes would fight them.
Col Ahmed Bani, a military spokesmen for the Benghazi-based rebel Transitional National Council, told the BBC: "This is misinformation. Gaddafi would never pull out of Misrata, it is too important too him."
He added: "We have just spoken to somebody from Misrata who is now in Benghazi - a member of the Bushaala tribe, one of the largest in Misrata.
"He says that the claims by the Gaddafi government are not true. All local tribes are fighting against Gaddafi's troops, not with them."
A doctor in Misrata told the BBC it was just a move to buy time.
"The spokesman is totally ridiculous. He just wants people to think the Libyan people are behind the regime," he said.
"If Gaddafi arms the people of Libya in the towns around Misrata, it will be the end for him, because they will rise up against him."
The doctor said the humanitarian situation was improving, but not significantly.
The BBC's Jeremy Bowen reports from Tripoli that the regime says the reason Col Gaddafi has remained relatively secure in the west of Libya is that the principal tribes - which wield a lot of power and influence - are on his side.
However, the government has previously used the prospect of tribal civil war as a warning, and it may well be that the minister was making more of a threat than expressing the reality of what is going to occur, our correspondent says.
The regime is feeling increasingly isolated and is hoping for some kind of a diplomatic solution, he adds.
The popular revolt against Col Gaddafi - inspired by similar uprisings in Egypt and Tunisia - began in February and a UN mandate later sanctioned air strikes against Libyan state forces to protect civilians. Nato took full command of the mission on 31 March, and since then more than 3,000 sorties have been flown.