US president Barack Obama has approved the use of armed drones in Libya, authorising US airstrikes against ground forces for the first time since America turned over control of the military operation to NATO.
Close on the heels of that announcement, Senator John McCain of the US has arrived in Benghazi on Friday for talks with the rebels fighting to overthrow Muammar Gaddafi.
The US senator is one of the strongest proponents in Congress of US military intervention in Libya.
Al Jazeera's Sue Turton reporting from Benghazi quoting McCain said he was there to meet the Transitional National Council and members of the military to assess the situation on the ground.
Speaking to our correspondent while walking out of a local hotel, he also denied concerns about the possibility of extremist or al-Qaeda elements fighting alongside the rebel forces, saying "they [rebel fighters] are my heroes".
The first armed drone mission since Obama's go-ahead was flown on Thursday, but the aircraft, armed with Hellfire missiles, turned back due to poor weather conditions without firing any of its munitions.
Predator drones have routinely been flying surveillance missions in Libya, Robert Gates, the US defence secretary, told reporters at a Pentagon briefing on Thursday.
He said the US will provide up to two 24-hour combat air patrols each day by the unmanned Predators.
Marine General James Cartwright, vice chairman of the Joint Chiefs of Staff, said the drones can help counteract the pro-Muammar Gaddafi forces' tactic of traveling in civilian vehicles that make it difficult to distinguish them from rebel forces.
"What they will bring that is unique to the conflict is their ability to get down lower, therefore to be able to get better visibility on targets that have started to dig themselves into defensive positions," Cartwright said.
"They are uniquely suited for urban areas."
He added, "It's very difficult to pick friend from foe. So a vehicle like the Predator that can get down lower and can get IDs better, helps us."
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Gates rejected the notion that the approval of drone strikes means that the US will get pulled slowly back into a more active combat role, despite Obama's vow merely to provide support for NATO.
US forces played a lead role in the early days of the conflict, launching an onslaught of cruise missiles and bombs against Gaddafi's surface-to-air missile sites and advancing Gaddafi's troops.
With American forces stretched by the wars in Iraq and Afghanistan, as well as the humanitarian operations in Japan, the Pentagon turned the mission over to NATO, saying it would do only limited airstrikes to take out air defences.
The US, said Obama, no longer would do airstrikes to protect the civilian population.
Gates said that bringing in the Predators will give NATO a critical capability that the US uniquely can contribute.
"I think this is a very limited additional role on our part, but it does provide some additional capabilities to NATO," said Gates.
"And if we can make a modest contribution with these armed Predators, we'll do it. ... I don't think any of us see that as mission creep."
He said Obama has been clear that there will be no US boots on the ground, and the main strike role would belong to the allies.
Gates, who publicly expressed skepticism about getting involved militarily in Libya before Obama endorsed the limited intervention, said "the real work" of overthrowing Gaddafi will have to be done by the Libyans themselves.
While he acknowledged the conflict "is likely to take a while," Gates also said the continuing sanctions, arms embargo and NATO-led offensive have weakened Gaddafi's military and eaten away at his supplies and cash.
Over the long term, Gates said, that will hurt Gaddafi's ability to strike back at opposition forces, if they should rise up again in other cities.
At the same time, however, Gates said the administration's decision to provide $25m in nonlethal military assistance to the rebels did not signal a deeper US commitment to anti-Gaddafi forces whose makeup, objectives and motives still are not fully understood in Washington.
The aid, he said, is not high-end military equipment but rather a hodge-podge of things like uniforms and canteens.
Asked how long he believes it will take the NATO-led air campaign to succeed, Gates replied, "The honest answer to that is, nobody knows."
Al Jazeera's Mike Hanna reports on the heavy street fighting in the eastern city of Misurata
Meanwhile, casualties are on the rise as Libyan government forces and rebel fighters battle it out on the streets of besieged western city of Misurata, amid calls by the UN chief to "stop fighting".
Ban Ki-moon, the UN secretary-general, urged Libyan authorities on Thursday to "stop fighting and stop killing people" and said the world body's priority was to secure a ceasefire.
"At this time our priority is to bring about a verifiable and effective ceasefire, and then we can expand our humanitarian assistance, and we are going to engage in political dialogue," he said during an official visit to Moscow.
The Libyan rebels have been trying since mid-February to end Gaddafi's 41-year-old rule but have struggled against his more experienced and better equipped forces.
Border post captured
Earlier on Thursday, pro-democracy fighters took control of the Libyan side of a key border crossing with Tunisia, in a remote western region.
Witnesses said pro-Gaddafi forces abandoned their weapons and fled into Tunisia.
Elsewhere in the country, Libyan state television said, NATO forces struck the Khallat al-Farjan area of the capital Tripoli, killing seven people and wounding 18 others.
The report could not immediately be independently verified.
But NATO denied that any air raid had killed civilians, saying the target was a command and control bunker in a military compound.