NATO have launched more airstrikes through the night on the Libyan capital, Tripoli, after thousands of troops
loyal to Libyan leader Muammar Gaddafi advanced on and shelled the rebel-held western city of Misurata.
The offensive had followed a lull in NATO bombing of Tripoli on Wednesday, after 24 hours of some of the heaviest bombardments of the Libyan capital since air strikes began in March.
By the evening, loud blasts once again rocked central Tripoli and aircraft screeched overhead, resuming strikes.
It was not immediately clear what was targeted, however, NATO strikes appear to be repeatedly pounding the same set of targets: the sprawling Muammar Gaddafi compound in central Tripoli, a series of government buildings and radar installations and military bases on the outskirts of the capital.
The fresh assaults came as the Obama administration challenged five key military allies to take on a greater share of the NATO-led air campaign against Gaddafi's forces, illustrating the strains of a three-month intervention in Libya that has no time frame for an exit.
The alliance says the bombing aims to protect civilians from the Libyan leader's military, which crushed popular protests against his rule in February, leaving many dead. The conflict has now become a civil war.
Robert Gates, the defence secretary, speaking in Brussels at a two-day session of NATO defence ministers, said Spain, Turkey and the Netherlands should enhance their limited participation in non-combat operations by joining in strike missions against ground targets.
US officials said that Gates alss pressed Germany and Poland, the two countries not participating at all militarily, to help in some form.
Eight NATO members are participating in air strikes in Libya: the US, Britain, France, Belgium, Canada, Norway, Denmark and Italy.
Misurata under attack
Earlier on Wednesday, thousands of troops loyal to Gaddafi, advanced on the rebel-held western city of Misurata, shelling it from two sides, in attacks that have reportedly killed at least 12 rebels.
"He has sent thousands of troops from all sides and they are trying to enter the city. They are still outside, though," Hassan al-Misrati, a rebel spokesman, told Reuters from inside the town.
Al Jazeera correspondent Tony Birtley, reporting from Misurata, said Gaddafi troops have shelled the city’s frontline.
"In a two-pronged attack, forces loyal to Gaddafi have attacked in the west as well as east of the city," he said.
"As per reports there has been heavy casualty on the sides of the rebels."
Our correspondent said: "We have also been told that the Gaddafi troops have fired grad rockets and Milan wire-guided missiles.
"There has been non-stop firing and landings of grad rockets throughout the day but no NATO strikes have taken place at the moment."
"Probing attacks are being made by Gaddafi forces in the last couple of days but they have been pushed back."
ICC Rape probe
Meanwhile, the chief prosecutor for the International Criminal Court said on Wednesday he was investigating whether Gaddafi provided Viagra-type drugs to Libyan soldiers to promote the rape of women during the current conflict.
Luis Moreno Ocampo said his office had "information that there was a policy to rape in Libya those who were against the government."
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He told a news conference in New York after briefing the UN Security Council on Darfur that some witnesses confirmed the Libyan government was buying containers of Viagra-type drugs to carry out the policy, and "to enhance the possibility to rape."
"We are trying to see who was involved," Moreno Ocampo added.
He said it was difficult to know how widespread the use of rape is in Libya.
The UN Security Council voted unanimously on February 26 to refer the Libyan crisis to the International Criminal Court, the world's permanent war crimes tribunal.
On May 16, Moreno Ocampo asked judges to issue arrest warrants for Gadhafi, his son Seif al-Islam Gadhafi and intelligence chief Abdullah al-Sanoussi, accusing them of committing crimes against humanity by targeting civilians in a crackdown against rebels who are trying to end his more than 40 year rule.
Judges are now evaluating the evidence and must decide whether to confirm the charges and issue international arrest warrants.
If the arrest warrants are issued, Moreno Ocampo said he may add the charge of rape to the case.