Reports are emerging this evening of military aircraft attacking crowds of anti-government protesters in the Libyan capital.
A Libyan man, Soula al-Balaazi, who said he was an opposition activist, told Al Jazeera television that Libyan air force warplanes had bombed "some locations in Tripoli".
He said he was talking from a suburb of the city.
No independent verification of the report was immediately available.
Egypt's army said it had set up two field hospitals and also camps to receive Egyptians on the border with Libya, after increasingly bloody battles between Libyan security forces and protests.
UN Secretary General Ban Ki Moon said he had an extensive discussion with Col Gadafy today, condemning the escalating violence in Libya and telling him it "must stop immediately," a UN spokesman said.
Meanwhile, the staff of Libya's mission to the United Nations declared allegiance to the people of Libya, instead of to its government led by Col Gadafy, a mission spokesman said this evening.
"The members of the Libyan mission are representing only the Libyan people and not anyone else," the spokesman, Dia al-Hotmani, said by telephone.
Two Libyan Air Force fighter pilots defected today and flew their jets to Malta where they told authorities they had been ordered to bomb protesters, Maltese government officials said.
They said the two pilots, both colonels, took off from a base near Tripoli. One of them has requested political asylum.
Earlier, British foreign secretary William Hague said today he had seen some information to suggest Col Gadafy may have fled the country and was on his way to Venezuela.
"You asked me earlier about whether Colonel Gadafy is in Venezuela," he told reporters on the sidelines of a European Union foreign ministers' meeting in Brussels.
"I have no information that says he is, but I have seen some information that suggests he is on his way there at the moment."
Diplomats said Mr Hague was not referring to rumours circulating in the media about Col Gadafy's whereabouts, but to separate sources for the information.
However, a senior source in president Hugo Chavez's government denied that Col Gadafy was on his way to Venezuela. Libyan Deputy Foreign Minister Khalid Kayem also denied reports he had fled.
"This news is groundless. It has no basis," he said on state television.
Earlier, Col Gadafy's justice minister Mustafa Mohamed Abud Al Jeleil has resigned over "the excessive use of violence against government protesters," Libya's privately-owned Quryna newspaper has reported.
The newspaper said on its internet site it had spoken to the minister by telephone. There was no immediate official confirmation of the resignation.
Col Gadafy's four-decade-old rule appeared in increasing jeopardy today as anti-government protests reached the capital for the first time, leaving dozens dead at the hands of the security forces.
Several cities in the east appeared to be in the hands of the opposition as protests spread from Benghazi, cradle of a popular uprising that has rattled one of the Arab world's most entrenched governments.
One of Col Gadafy's sons said the veteran leader would fight the revolt until "the last man standing".
Protesters rallied in Tripoli's streets, tribal and religious leaders spoke out against Col Gadafy, and army units defected to the opposition in a revolt that has cost the lives of more than 200 people.
Protesters said they had taken control of Benghazi and other cities, with some analysts suggesting the country was heading for civil war.
"Libya is the most likely candidate for civil war because the government has lost control over part of its own territory," said Shadi Hamid, director of research at the Brookings Doha Centre in Qatar.
In India, Libya's ambassador said he was resigning in protest at the violent crackdown.
A coalition of Libyan Muslim leaders told all Muslims it was their duty to rebel against the Libyan leadership because of its "bloody crimes against humanity".
In India, Libya's ambassador said he was resigning in protest at the violent crackdown.
European nations watched developments in Libya with a growing sense of alarm after the government in Tripoli said it would suspend cooperation on stemming the flow of illegal immigrants across the Mediterranean.
British prime minister David Cameron, on a visit to the region, said events in Libya were appalling and unacceptable.
Al Jazeera television quoted medical sources as saying 61 people had been killed in the latest protests in Tripoli.
It said security forces were looting banks and other government institutions in Tripoli, and protesters had broken into several police stations and wrecked them.
A reporter in Tripoli said residents were stocking up on essential goods, apparently in anticipation of new clashes after nightfall. There were long queues at food shops and long lines of cars at fuel stations.
The building where the General People's Congress, or parliament, meets in Tripoli was on fire today, as was a police station in one of the eastern suburbs.
Gadafy's son Saif al-Islam Gadafy appeared on national television in an attempt both to threaten and to calm people, saying the army would enforce security at any price to put down one of the bloodiest revolts to convulse the Arab world.
"We will keep fighting until the last man standing, even to the last woman standing," he said yesterday.
But people in Tripoli expressed anger at the speech. A Libyan woman who gave her name as Salma, said: "The speech was very, very bad."
"The speech was very disappointing because he threatened the Libyan people with killing, hunger and burning. He did not offer mercy for the souls of the martyrs who were killed."
Another man said: "We were waiting for something good for us, the young people, to calm the anger but he did nothing."
Col Gadafy's supporters were in central Tripoli's Green Square today, waving flags and carrying his portrait.
Saif al-Islam's cajoling is unlikely to be enough to douse the anger unleashed after four decades of rule by Col Gadafy - mirroring events in Egypt where a popular revolt overthrew the seemingly impregnable president Hosni Mubarak 10 days ago.
Reuters