ROME (Reuters/AFP) - At least 40 civilians have been killed in air strikes by Western forces on Tripoli, the top Vatican official in the Libyan capital told a Catholic news agency on Thursday, quoting witnesses. The so-called humanitarian raids have killed dozens of civilian victims in some neighborhoods of Tripoli, said Giovanni Innocenzo Martinelli, the Apostolic Vicar of Tripoli. I have collected several witness accounts from reliable people. In particular, in the Buslim neighborhood, due to the bombardments, a civilian building collapsed, causing the death of 40 people, he told Fides, the news agency of the Vatican missionary arm. Libyan officials have taken foreign reporters to the sites of what they say were the aftermath of Western air strikes on Tripoli but evidence of civilian casualties has been inconclusive. Western powers say they have not confirmed evidence of civilian casualties from air strikes, which they have carried out under a UN mandate to protect civilians caught in conflict between Libyan leader Muammar Gaddafis forces and rebels. Its true that the bombardments seem pretty much on target, but it is also true that when they hit military targets, which are in the middle of civilian neighborhoods, the population is also involved, Martinelli said. Yesterday I said that bombardments had hit, albeit indirectly, some hospitals. To be precise, one of these hospitals is in Mizda, he said, mentioning a town about 145 km southwest of the capital. Meanwhile, NATO has launched a probe to determine whether the alliance was involved in any air raid that may have killed civilians, the general in charge of the operations said Thursday. Lieutenant General Charles Bouchard said he was aware of news reports citing a Tripoli-based Italian Catholic bishop who said that 40 civilians died when a building collapsed during a bombing in the Buslim district of Tripoli. We are investigating and we will report the details once the investigation is completed, Bouchard told reporters via videolink from his headquarters in Naples, Italy. My investigation is to ascertain whether or not NATO forces were involved in this incident, he said. Libyan leader Moamer Gaddafi suffered a major blow with the defection of his foreign minister, as his forces Thursday bombarded a rag-tag rebel army and NATO ruled out sending them arms. AFP reporters said running battles raged Thursday on the edge of Brega, with Gaddafi's forces shelling the insurgents who returned fire with Grad rockets and rocket-propelled grenades. A day after Gaddafi's forces overran the key oil hub Ras Lanuf and neighbouring villages, the frontline ebbed and flowed on the outskirts of Brega, about 800 kilometres from Tripoli. Artillery shells thumped across the desert north of the road, sending up black clouds of smoke, as the rebels responded with a barrage of Grad rockets that flared through the sky before disappearing off in the distance. Clashes also ensued around an oil terminal, but it was unclear who was in control of the town, which the rebels had seized back at the weekend, only to lose again on Wednesday. As a debate raged over whether Western powers should arm the insurgents, NATO chief Anders Fogh Rasmussen said in Stockholm such a move was beyond the scope of the alliance. We are there to protect the Libyan people, not to arm people, Rasmussen told reporters. Western strikes have damaged the Libyan regimes forces but Gaddafi's army is not about to break, the US militarys top officer told lawmakers in Washington. Admiral Mike Mullen said at least 20 percent of the regimes military had been knocked out but that does not mean hes about to break from a military standpoint. Also in Washington, US Defence Secretary Robert Gates said that economic and political pressure and Libyas people rather than the military strikes will eventually drive strongman Gaddafi from power. France, which on Tuesday had indicated it was ready to discuss sending arms shipments to the insurgents, on Thursday ruled out such a step, saying it is not compatible with a UN resolution on the conflict. Libyas rebels meanwhile are treating as classified any talks or moves it is now making to procure weapons from foreign powers, a spokesman told reporters in their stronghold of Benghazi Thursday. The defection of foreign minister Mussa Kussa, the most senior figure to jump ship since the uprising against Gaddafi's iron-clad 41-year rule erupted more than six weeks ago, was widely seen as an indication that the strongmans regime is crumbling. Kussa arrived at Farnborough Airfield, west of London, on Wednesday, a Foreign Office statement said. British Foreign Secretary William Hague insisted that Kussa, who has been blamed for atrocities including the 1988 Lockerbie bombing, had not been offered immunity from prosecution in British or international courts. He told reporters the minister was being interviewed voluntarily by British officials. In Tripoli, the Libyan government confirmed the resignation of Kussa and said he was allowed to leave the country for medical treatment in neighbouring Tunisia. As Western leaders plotted his downfall, Libyas eccentric leader warned that they had started something in Libya which they cannot control. They have started something dangerous, something they cannot control. It will be out of their control no matter what methods of destruction they have at their disposal, Gaddafi said.