Colonel Muammar Gaddafi appeared on Libyan state television last night to insist that his 42-year rule over the country remained intact.

As violence escalated in the capital, Tripoli, his foreign diplomats disowned him as a war criminal and elements of his feared security forces defected.

"I'm not in France, I'm not in Venezuela, I'm still here," he declared, while seated in the passenger seat of a car holding an umbrella up through the open door. The short clip was broadcast after a day of rumours about his whereabouts. Eyewitnesses and news reports had earlier said elements loyal to the regime were firing on protesters in Tripoli. Opposition leaders prepared for another night of defiance and called for crowds to occupy the city's vast Green Square.

Hundreds of people have died as the regime has attempted to stamp out six days of protests in several cities across the country. In the capital yesterday Gaddafi loyalists deployed snipers and roadblocks and, according to some witnesses, warplanes and helicopters.

Reports from inside the country continued to be confused last night, but outside Libya it seemed that the longest-established regime in the Arab world was crumbling. Emboldened, Libya's ambassadors to the United Nations called for Colonel Gaddafi to step down, joining a string of diplomats who have defected.

Last night, Colonel Gaddafi's grip on power appeared to be further weakened when a group of Libyan army officers issued a statement urging fellow soldiers to "join the people" and help to rid the country of their leader.

The disowning that began on Sunday with Abdel-Moneim al-Houni, Libya's ambassador to the Arab League in Cairo, continued with diplomats in China, New York and elsewhere demanding that Colonel Gaddafi quit. "We are sure that what is going on now in Libya is crimes against humanity and crimes of war," the country's deputy permanent representative to the United Nations, Ibrahim Dabbashi, said. At a hastily arranged press conference in the lobby of the Libyan Mission in New York, under a giant portrait of Colonel Gaddafi, the diplomat called on the leader to resign. He said: "We find it is impossible to stay silent and we have to transfer the voice of the Libyan people to the world."

The growing feeling of discontent was matched by foreign diplomats. Issuing a statement, the US Secretary of State, Hillary Clinton, condemned the violence, saying that the world was watching the situation: "The government of Libya has a responsibility to respect the universal rights of the people, including the right to free expression and assembly. Now is the time to stop this unacceptable bloodshed. We are working urgently with friends and partners around the world to convey this message to the Libyan government."

The UN secretary general, Ban Ki-moon, was said to have had an "extensive" telephone discussion with Colonel Gaddafi yesterday concerning the deteriorating situation in the country and "expressed deep concern at the escalating scale of violence and emphasised that it must stop immediately".

The regime has banned foreign journalists, leaving outsiders to rely on fragmented reports, such as an eye-witness account from Soula al-Balaazi, a Libyan man who told the Al Jazeera television network that he was an opposition activist. He said that Libyan warplanes had bombed "some locations in Tripoli". Others described seeing foreign-born mercenaries firing on crowds in the capital.

Libya's second city, Benghazi, flew the flag of the former monarchy toppled in 1969 yesterday, as protesters claimed to have "liberated" it after bloody clashes that left scores of people dead and hospitals overwhelmed with the injured. "Gaddafi needs one more push and he is gone," Amal Roqaqie, a lawyer at the Benghazi court, told the Associated Press, adding that protesters were "imposing a new reality" and would install a "transitional government".

Reports of defections abounded. Two Libyan air force colonels landed at Malta international airport in Mirage fighter jets after flying low across Libya to avoid detection and then communicating their request for asylum to air traffic control in Malta.

The scale of the shock inside a regime that has taken all of its orders from the top and learnt to live with the capricious whims of Colonel Gaddafi was clear from a rambling and contradictory television appearance by his son, Saif, in the early hours of yesterday. Saif gave a confused 40-minute speech which attempted to offer reforms while warning that further protests would result in a civil war in which Libya's oil wealth "will be burned".

The international community has spent recent years building bridges with the unpredictable, but seemingly entrenched, regime – only to see it teeter towards collapse in mere days.

Belfast Telegraph