Libyan rebels claimed Sunday the endgame had come for the fight to take over Tripoli, while Libyan leader Muammar Gaddafi dismissed reports that he has left the besieged capital.

Abdel Hafiz Ghoga, vice-chairman of the Benghazi-based rebel National Transitional Council (NTC), said "the zero hour has started" and that rebels in Tripoli have "risen up" in coordination with the NTC.

According to Al Jazeera, sustained gunfire and explosions have been rocking Tripoli overnight, and the fighting inside the capital prompted celebrations among rebels and Western media's speculation that Gaddafi's 41-year rule might be approaching the end.

But Gaddafi's officials insisted early Sunday the Tripoli revolt had been crushed, a few hours after it began.

Gaddafi's spokesman, Moussa Ibrahim, told state press that a small number of rebel forces had infiltrated the capital, but had been dealt with. He said the city is safe.

But Bashir Sewehli, a Libyan activist, told Al Jazeera that the clashes in Tripoli are still going on.

"The military airport is under control of the rebels, and there are other areas in and around Tripoli as well. The rebels are waiting for reinforcements," he said.

"The news has not been coming through because of the fighting, but we will know more in the next coming hours," he added.

BBC correspondent Matthew Price wrote from Tripoli via his Twitter account that the situation there "did go quiet for a bit but appears it was a lull. Sounds of heavy fire now and explosions..."

Though embattled, Gaddafi remained defiant as he delivered a speech on state television in the early hours of Sunday.

In the audio message, he blamed the rebels for burning and destroying "everything" in the country, which was something unacceptable in the holy Ramadan month.

He said the rebels' deeds were all "scandals" under the guise of democracy, and he called the opposition "traitors" who didn't represent Libya. He also urged his supporters to start their search for the "rats."

During the speech, Gaddafi said he was now in Tripoli, rejecting reports that he had fled town.

But a senior rebel official said Gaddafi made the speech via satellite phone and was not in the capital.

Anticipating that, Gaddafi said "they (the rebels) will say this message is recorded... It's Sunday, the 21st of August. Time is 1:37 in Libya time."

Later on, Gaddafi's son Seif al-Islam vowed in a pre-recorded speech aired by the state TV not to "abandon the fight," saying the government forces "will resist for six months, one year, two years" until victory.

But he also signaled that the government is ready for talks with the rebels."If you want peace, we are ready."

Hours after capturing the key city of Zawiya 50 km west of Tripoli on Saturday, the rebels launched assaults on the capital, helped along by heavy NATO airstrikes that started after nightfall.

The Libyan rebels' military spokesman Col. Ahmed Bani confirmed to Xinhua that the rebels have taken control of the Tripoli International Airport and a weapons depot in the capital.

Rebel sources also said their forces have taken control of most of the Tajura district in eastern Tripoli and laid siege to the Mitiga airbase.

The rebels also battled with government troops in the suburb of Qadah and elsewhere, leaving an unknown number of casualties.

Despite the rebels' push toward the capital, the rebel military spokesman told reporters that the rebels had retreated from the industrial section of the strategic oil port of Brega, a day after capturing it from Gadaffi's troops.

U.S. media reported vacationing President Barack Obama is following the latest developments in Libya, being kept up to date by aides.