Muammar Gaddafi refused to step down as Libya's leader in a televised address on Tuesday afternoon saying "I am going to die here as a martyr" and accusing "forces affiliated to foreign forces" of seeking to "disfigure, undermine and tarnish the reputation of the country".

The dictator said he would not to give up power and attacked "the tyranny of the US" and other countries.

"We shall remain here and defiant," he said, calling on supporters to take to the streets to back him on Wednesday.

Gaddafi, dressed in brown robes and pounding his fist, accused "sick people within the nation" of trying to seduce others into rebellion with money and drugs. "This is my country, watered by our blood and your blood," he said.

His defiance came as the United Nations security council met in closed session to discuss his brutal crackdown in Libya. There were fears of a bloodbath following Gaddafi's earlier appearance in the capital city, Tripoli, to deny he had fled the country.

Libya's deputy ambassador to the UN, Ibrahim al-Dabashi, appealed for international intervention, starting with a no-fly zone over the country, to help stop "a real genocide".

Rebel soldiers claimed they had seized control of eastern Libya and blasts were heard in the city of Tobruk as the UN refugee agency urged Libya's neighbours to give refuge to those fleeing the violence.

"All the eastern regions are out of Gaddafi's control now ... The people and the army are hand-in-hand here," said a former army major Hany Saad Marjaa.

Runways at Benghazi airport have been destroyed in the violence, according to the Egyptian authorities. The country's second city has been the scene of alleged massacres in recent days.

The death toll in Libya passed 250 on Monday after six days of unrest, but this is a conservative estimate. The International Federation of Human Rights estimated the death toll of up to 400.

Parts of Tripoli were attacked by fighter jets and helicopter gunships overnight. Twenty-six people also died in the eastern city of Al Bayda as it came under fire from forces using aircraft and tanks, according to one eyewitness report.

British Airways and bmi have cancelled flights from Heathrow to Tripoli, while the Dutch airline KLM and the Arab carrier Emirates are among other companies to have also suspended services in and out of the Libyan capital. The Foreign Office is reviewing its advice to Britons without "pressing need to remain" to leave by commercial means, if safe to do so.

During the protests in Egypt, the UK laid on a charter flight and was urgently looking into similar options as the Libyan crisis deepened.

The Ministry of Defence is investigating whether naval forces could rescue stranded Britons. The frigate HMS Cumberland is remaining in the Mediterranean instead of returning to the UK to be scrapped. But Libyan ports are said to be closed. "We are monitoring the situation closely. The safety and security of British nationals are our top priority," said a MoD spokeswoman

Gaddafi appeared briefly on Libyan state TV on Monday to deny reports that he had fled the country. "I want to show that I'm in Tripoli and not in Venezuela. Do not believe the channels belonging to stray dogs," he said, holding an umbrella in the rain and leaning out of a vehicle. The station said he was speaking outside his house.

As his forces launched air strikes against protesters amid apparent confirmation of claims that African mercenaries were being used to quell the violence, the UN secretary general, Ban Ki-moon, condemned the "very disturbing and shocking scenes". He said he had spoken to Gaddafi and "forcefully urged him to stop violence against demonstrators". Ban told reporters: "This is unacceptable. This must stop immediately. This is a serious violation of international humanitarian law."

The Arab League is to hold an emergency meeting in Cairo. At least seven Libyan ambassadors have resigned in protest over the killings, although other senior diplomats remained in their post while appealing for Gaddafi to step down.

In New York, Dabashi said there must be a no-fly zone "on the cities of Libya so no mercenaries, no supplies of arms will arrive to the regime". He told a press conference that he and other UN diplomats were not resigning because they served the people of Libya, not the regime.

"This is in fact a declaration of war against the Libyan people," he said, while surrounded by a dozen Libyan diplomats. "The regime of Gaddafi has already started the genocide against the Libyan people."

Libya's ambassador to the US, Ali Aujali, said he was resigning; he had previously said he was not quitting his post because he was "on the "good side" of the Tripoli government.

He told ABC's Good Morning America: "This regime is shaking and this is the time to get rid of it. Please, please, help the Libyan people. Help them. They are burning. We need the world to stand up by us … I resign from serving the current dictatorship regime. But I will never resign from serving our people until their voices reach the whole world, until their goals are achieved."

Libya's ambassador at the UN, Abdurrahman Mohamed Shalgham, told the pan-Arab newspaper, al-Hayat, that all diplomats at Libya's mission supported Dabashi, "excluding me". Shalgham said he was in touch with the Gaddafi government and was trying "to persuade them to stop these acts".

The country's ambassador to India, who resigned over the crackdown, said African mercenaries were being employed by Gaddafi. "They are from Africa, and speak French and other languages," Ali al-Essawi told Reuters, adding he had been told there had been army defections.

"They [the troops] are Libyans and they cannot see foreigners killing Libyans so they moved beside the people."

In Al Bayda, resident Marai Al Mahry told Reuters by telephone that 26 people, including his brother Ahmed, had been shot dead overnight by Gaddafi loyalists. "They shoot you just for walking on the street," he said.

"The only thing we can do now is not give up: no surrender, no going back. We will die anyway, whether we like it or not. It is clear that they don't care whether we live or not."