Libya: Nato strikes hit eight Gaddafi warships in ports
Nato air strikes have hit eight warships belonging to Col Muammar Gaddafi's forces in co-ordinated raids on Tripoli, Al Khums and Sirte.
In a statement, a spokesman said Nato had to take "decisive action" given Col Gaddafi's increasing use of naval assets to launch attacks on civilians.
Flames and smoke could be seen rising from vessels hit in the capital's port.
Meanwhile, the Libyan rebel leadership has appealed for international help for towns in the mountains west of Tripoli.
The alliance statement said the use of indiscriminate mining by pro-Gaddafi maritime forces had disrupted the flow of much-needed aid into Libya and had also "demonstrated a clear intent to attack Nato forces".
It said the strikes on Friday demonstrated Nato's "resolve to protect the civilian population of Libya, using appropriate and proportionate force".
"All the vessels targeted last night were naval warships with no civilian utility," said Rear-Adm Russell Harding, Deputy Commander of Nato's mission in Libya.
It was unclear if there were any casualties.
The Nato air strikes are being carried out under a UN mandate to protect civilians from the forces of Col Gaddafi, who is trying to crush the three-month-old uprising.
'Short of water'
Nato Secretary General Anders Fogh Rasmussen said earlier on Thursday that Col Gaddafi's forces were suffering under the attacks and becoming more isolated every day.
"We have significantly degraded Gaddafi's war machine and now we see the results - the opposition has gained ground," he said.
The rebels' National Transitional Council, based in Benghazi, has appealed for international help for towns in the Nafousa mountains, south west of Tripoli.
Ahmed Bemoussa, a council member who visited the region, said people there were under constant bombardment from Col Gaddafi's forces and had run out of water.
Mr Bemoussa said Nato strikes in the region appeared to be doing little to halt the attacks, and appealed for the establishment of an internationally monitored corridor to bring in aid.
Restrictions on reporting in Libya mean such accounts are hard to verify.
But the BBC's David Loyn in Benghazi says that if Mr Bemoussa is to be believed, conditions in the mountain region have become are as bad as during the worst days of fighting in the coastal town of Misrata last month.
On Thursday, US President Barack Obama said "time is working against Gaddafi" and that he does not have control over his country.
In a major speech to the State Department. Mr Obama said the Libyan opposition has organised a "legitimate and credible interim council".
"When Gaddafi inevitably leaves or is forced from power, decades of provocation will come to an end, and the transition to a democratic Libya can proceed."
Libyan government spokesman Moussa Ibrahim said Mr Obama's comments were "delusional".
"He believes the lies that his own government and media spread around the world. It's not Obama who decides whether Muammar Gaddafi leaves Libya or not. It's the Libyan people."