NEAR AJDABIYA, Libya (AFP/Reuters) - Libyan ground troops are being targeted by airstrikes, coalition officials said on Wednesday, as a top British officer declared Moamer Gaddafis air force effectively destroyed. As bitter fighting raged in key rebel strongholds, six NATO warships backed up by aircraft began patrolling international waters off Libyas coast to enforce a UN arms embargo against Gaddafis regime, the alliance said. Air Vice Marshal Greg Bagwell of Britain said that Libyas air force has been almost totally destroyed by the airstrikes and no longer exists as a fighting force. Bagwell told British media at an airbase in southern Italy, from which RAF warplanes are operating, that Libyan ground forces were also being attacked when they threaten civilians. The US military also said Gaddafis ground troops who are threatening rebel-held cities are now being targeted by coalition airstrikes. We are putting pressure on Gaddafis ground forces that are threatening cities, Rear Admiral Gerard Hueber, US chief of staff for the Libya mission, told journalists. Asked if that meant airstrikes, he replied: Yes. However, there was no immediate sign of coalition assistance at two flashpoints where rebels are battling Gaddafis forces - Ajdabiya, south of the rebel capital of Benghazi, and Misrata, Libyas third city 214 kilometres east of Tripoli. We will not surrender, Gaddafi told supporters forming a human shield to protect him at his Tripoli compound, which came under attack in 1986 from the US Reagan administration and once again in the current round of air raids. There were no reports of civilian casualties caused by Western airstrikes, said Rear Admiral Gerard Hueber, a top US military officer involved in enforcing the no-fly zone. But neither had Libyan forces pulled back from Misrata, he said. There have been no reports of civilian casualties. Our mission here is to protect the civilian populace and we choose our targets and plan our actions with that as a top priority, he told reporters by phone from the command ship USS Mount Whitney in the Mediterranean. Rebels also said they had been under intense attack in their Misrata enclave, which has been besieged by Gaddafi forces for weeks, with a doctor saying 17 people were killed on Tuesday by snipers and shelling. Early on Wednesday, CNN reported coalition airstrikes launched overnight near Misrata. Coalition forces are acting under UN Security Council Resolution 1973 authorising all necessary means to protect civilians fighting to topple Gaddafi, including enforcing a no-fly zone. In Berlin, Beverly Mock, spokeswoman for the coalition, said 97 sorties were carried across Libya in the course of the 24 hours ending 1200 GMT on Wednesday. No cruise missiles were fired in the period but airstrikes targeted tanks, anti-aircraft batteries and command centres, Mock said, without elaborating. US Defence Secretary Robert Gates said in Cairo that there was no timeline for when UN-backed military operations in Libya would end. The no-fly zone is not time limited by the Security Council resolution. So I think that there is no current timeline in terms of when it might end, Gates told reporters. In Paris, an envoy from the rebels transitional council said their objective was a regime that would be democratic and secular. Mansour Saif al-Nasr also predicted that Gaddafi would fall quickly, opening the way for a rebuilding of society. Six NATO warships backed up by aircraft began Wednesday to patrol international waters off Libyas coast to enforce a UN arms embargo against Moamer Gaddafis regime, the alliance said. NATO warships and aircraft have started patrolling the approaches to Libyas coast as part of Operation Unified Protector, NATO said on its website. The ships were already in international waters off Libyas coast while patrol aircraft and fighter jets were heading to the area to provide long-range surveillance and intercept any suspected flights carrying weapons into Libya, it said. The ships will remain in international waters and will not enter Libyan territorial waters, NATO said. Alliance General Pierre St-Amand of Canada said earlier that six NATO nations have pledged 16 vessels for the operation, including three submarines. Meanwhile, three journalists including two Agence France-Presse employees held by Gaddafis forces since the weekend were released in Tripoli early Wednesday. Dave Clark, Roberto Schmidt, and Getty photographer Joe Raedle were arrested on Saturday. Gaddafi forces resumed their bombardment of Zintan, another rebel-held town in west Libya, a resident said, and tanks were expected there. Gaddafis brigades started bombardment from the northern area half an hour ago. The bombardment is taking place now. The town is completely surrounded. The situation is very bad, the resident, Abdulrahman, told Reuters by telephone from the town. Turkish President Abdullah Gul said Wednesday that some countries in the coalition striking Libya are driven by opportunism and have prompted suspicions of secret intentions in the oil-rich country. Foreign ministers from the coalition taking military action against the Libyan regime and from regional countries will meet in London on Tuesday, the British foreign ministry confirmed. Confirming an earlier announcement by France, British Foreign Secretary William Hague said they would form a contact group of nations to advance efforts to stop Moamer Gaddafis forces killing civilians. The European Union tightened the noose on Moamer Gaddafis regime Wednesday, slapping new sanctions on the Libyan oil sector and banning aircraft suspected of carrying mercenaries from EU airspace. In a fourth wave of EU sanctions against Tripoli, the 27-nation bloc ordered an assets freeze on the National Oil Corp. and five of its subsidiaries as well as targeting a further 14 economic entities and 25 Gaddafi associates, diplomats said.