NATO warplanes have bombed Libyan naval vessels in three ports, leaving ships partially sunken and charred and showering docks with debris in the military alliance's broadest attack on Muammar Gadhafi's navy.

NATO said the bombing runs were meant to protect the nearby rebel-held port of Misrata, the only major city in the western half of Libya that is under the control of the fighters trying to end Gadhafi's nearly 40-year rule. One of the attacks struck the main port of Tripoli, and reporters could see flames and smoke pouring up into the night sky from stricken vessels.

Open gallery view A Libyan official inspects damage on naval ships moored at the sea port in Tripoli, Libya, Friday, May 20, 2011. Credit: AP

In a later tour of the area on Friday, journalists saw three partially submerged boats armed with missile launchers docked alongside one another. The blasts peeled away part of a gun turret. Altogether, eight coast guard boats and one docked frigate under repair were hit at the three ports, said Commandant Omran al-Forjani, head of Libya's coast guard.

At NATO headquarters in Brussels, the alliance confirmed its warplanes targeted the boats and accused Libya of using its ships in the escalating conflict, including attempts to mine the Misrata's harbor, a key lifeline to the besieged city. The other ports hit were in the city of Khoms, between Tripoli and Misrata, and in Sirte, farther east, Libyan officials said.

British Maj. Gen. John Lorimer, a NATO communications officer, said British warplanes hit two Libyan corvette warships in the Khoms harbor and successfully targeted a facility in the dockyard constructing fast inflatable boats, which Libyan forces have used several times in their efforts to mine Misrata and attack vessels in the area.

He said the port was the nearest concentration of regime warships to the port of Misrata, which Gadhafi has repeatedly attempted to close to humanitarian shipping.

Rear Adm. Russell Harding, deputy commander of the NATO operation, said the Gadhafi regime was employing more ships in its campaign against0rebel fighters.

Given the escalating use of naval assets, NATO had no choice but to take decisive action to protect the civilian population of Libya and NATO forces at sea, he said.

Libya countered the claims, saying it has left its ships docked since a NATO warning at the end of March that they would be considered targets if they left port.

We were told if the boats moved, they would be hit, said al-Forjani at a press conference in a cafe by the Tripoli port.

Al-Forjani said the boats hit were donated to the coast guard by Libya's navy and never carried missiles. He said they were used to patrol Libyan waters for boats carrying African migrants trying to make the dangerous sea crossing to Europe and for search-and-rescue operations.

Another government official accused NATO of trying to frighten commercial ships from using ports under the control of the Libyan government.

Mohammed Rashid, general manager of Tripoli's port, said only eight commercial ships had entered the port since the NATO airstrikes began on March 19. The slowdown in shipping could reduce imports and drive up the cost of basic goods for Libyans, he said.

This is a continuation of the humanitarian blockade that began before two months, he said.

In Brussels, NATO played video clips from the jets' gun cameras showing the bombing of two frigates and a port facility.

The two frigates, a Soviet-built Koni class anti-submarine boat and a French-built Combattante class missile craft, were moored at the dock when they were hit with laser-guided bombs. It was not immediately clear whether their crews were aboard when they were struck.

Our aim was not to destroy these ships but to remove their military ability, NATO spokesman Wing Cmdr. Mike Bracken told reporters. They were identified as legitimate and legal targets.

But Bracken declined to say whether the frigates had been used in any naval operations - such as the mining of Misrata port - in recent weeks. He said NATO has meticulously communicated to all government troops that the risks of being around military equipment were extremely high.

NATO is operating under a UN mandate to maintain a no-fly zone over Libya and to prevent attacks on the civilian population.

The Western coalition has stepped up its airstrikes in the Libyan capital in an apparent attempt to weaken Gadhafi's chief stronghold and potentially target the leader himself. The Gadhafi family compound on the Bab al-Aziziya military base has been targeted several times.

Also, a NATO strike early Friday hit a police academy in the Tripoli neighborhood of Tajoura, a government official said.

Libyan government spokesman Moussa Ibrahim told reporters at a late-night news

conference Thursday that in a meeting earlier this week with Russian leaders, an envoy offered to withdraw Libyan fighters from cities as part of a peace deal, if rebels do the same.

We are even prepared to go as far as withdrawing our army from all Libyan cities and population centers, he said. This is a new offer. Ibrahim said the offer was the farthest the government had gone since fighting broke out against the rebels. He said as part of the deal, NATO would also have to halt its strikes of Libyan targets.

A spokesman for the Benghazi-based National Transitional Council said the rebels would stop fighting only if Gadhafi complied with the UN resolution that authorized the establishment of a no-fly zone and demanded the immediate establishment of a cease-fire and a complete end to attacks on civilians.

As long as they implement the UN resolution to the letter - withdraw all troops to their barracks, release all political prisoners and allow people to demonstrate freely - we are willing to cease fire, Jalal Gallal told The Associated Press. But for long-lasting peace there is no solution that includes him (Gadhafi) and his family.

Asked if rebels would retreat from towns and cities, he said Retreat to where? We are in our homes.

Also Friday, French Foreign Ministry spokesman Bernard Valero said authorities in the rebel leadership council told France's ambassador that four French nationals held since May 11 are about to be taken to the border for release.

The ministry said last week that five Frenchmen were detained at a police checkpoint in Benghazi, and that one was shot and later died in the hospital. It provided no names for the five.