TRIPOLI - Explosions and gunfire rocked Tripoli overnight, after days of battlefield defeats left Muammar Gaddafi's government and troops penned ever more tightly in the besieged capital by a rebel advance.Rebels said the fighting marked a final push in an uprising against the long-time leader that has raged in the North African oil-producing nation for six months, while Gaddafi dismissed it as an ill-fated attempt by "rats".RELATED:Battle outside Libyan capital, fighting spills to TunisiaUS says "Gaddafi's days are numbered""Those rats ... were attacked by the masses tonight and we eliminated them," Gaddafi said in a live audio message over state television."I know that there are air bombardments but the fireworks were louder than the sound of the bombs thrown by the aircraft."An official at the rebel National Transitional Council said the fighting was the beginning of the end for Gaddafi."The zero hour has started. The rebels in Tripoli have risen up," Abdel Hafiz Ghoga, vice-chairman of the rebel National Transitional Council, based in the eastern Libyan city of Benghazi, told Reuters.The clashes inside the city triggered celebrations among Gaddafi opponents elsewhere in the country and in the capital of neighboring Tunisia, and fed widespread speculation Gaddafi's 41-year rule was sliding towards collapse. Gaddafi's information minister said the rebel incursion into Tripoli had been quickly put down, though sounds of gunfire and explosions continued into the early morning.Fighting was still raging after midnight around Mitiga airbase in Tripoli's Tajourah district, an area said to be under rebel control, an opposition activist told a Reuters journalist outside Libya.The gunbattles had left a number of rebels dead in the suburb of Qadah and elsewhere, along with at least three pro-Gaddafi soldiers in the Zawiyat al-Dahmania district of Tripoli, he said.A Tripoli resident told Reuters that imams, or Muslim clerics, in parts of Tripoli called on people to rise up, using the loudspeakers on minarets. The resident said the call went out around the time people were breaking their Ramadan fast.Earlier on Saturday evening, residents told Reuters of gunfire and street protests in several parts of Tripoli."We can hear shooting in different places," one residents said. "Most of the regions of the city have gone out, mostly young people ... it's the uprising... They went out after breaking the (Ramadan) fast.""They are shouting religious slogans: 'God is greatest!'" This week's rebel advances on Tripoli have transformed the war by cutting the capital off from its main road link to the outside world and putting unprecedented pressure on Gaddafi.