Heavy and sustained gunfire has broken out in the Libyan capital, Tripoli. A BBC correspondent said machinegun and heavy weapons fire could be heard across the city. It is not clear what the source of the fire was or who started it but it is the heaviest in Tripoli since the rebellion against Col Muammar Gaddafi began two weeks ago. There have been protests against Col Gaddafi's rule in Tripoli but the city has so far remained in his control. The BBC's Wyre Davies in Tripoli says the gunfire was heard all over the city, although authorities have been saying it is celebratory gunfire. Two residents who contacted the BBC said one key area in which gunfire had been heard was around the airport. The city has been Col Gaddafi's main stronghold as he attempts to reassert control over the country from rebels who have taken much of the east of the country as well as some towns closer to Tripoli, in the west. Residents of rebel-held Zawiya, 50km (30 miles) west of Tripoli, said Col Gaddafi's troops had fired indiscriminately on civilians on Saturday as they attempted to capture the town. And in the east, rebels said they were advancing westwards on Sirte, the heavily defended hometown of Col Gaddafi. Source: BBC