Protests against Gaddafi's rule have prompted harsh reprisals in several cities, including the capital Tripoli [Reuters]

Deep cracks were showing and Gaddafi seemed to be losing vital support, as Libyan government officials at home and abroad resigned, air force pilots defected and major government buildings were targeted during clashes in the capital.

At least 61 people were killed in Tripoli on Monday, witnesses told Al Jazeera. The protests appeared to be gathering momentum, with demonstrators saying they had taken control of several important towns and the city of Benghazi, to the east of Tripoli.

Protesters called on Monday for another night of defiance against Gaddafi, despite a harsh security crackdown by his government.

A huge anti-government march in Tripoli on Monday afternoon came under attack by security forces using fighter jets and live ammunition, witnesses told Al Jazeera.

Libyan authorities have cut all landline and wireless communication in the country, making it impossible to verify the report.

As violence flared, the Reuters news agency quoted William Hague, the British foreign secretary, as saying he had seen some information to suggest that Gaddafi had fled Libya and was on his way to Venezuela.

But Al Jazeera's Dima Khatib, reporting from the Venezuelan capital, Caracas, said government officials there denied that Gaddafi was on his way to the South American country.

With reports of large-scale military operations under way in Tripoli, a spokesperson for Ban Ki-moon said the UN chief held extensive discussions with Gaddafi on Monday, condemned the escalating violence in Libya and told him that it "must stop immediately”.

" ... The secretary-general underlined the need to ensure the protection of the civilian population under any circumstances. He urged all parties to exercise restraint and called upon the authorities to engage in broad-based dialogue to address legitimate concerns of the population,” Ban's spokesperson said.

For this part, several Libyan diplomats at the country's UN mission called on Gaddafi to step down.

Ibrahim Dabbashi, the deputy ambassador, said that if Gaddafi did not relinquish power, "the Libyan people [would] get rid of him”.

"We don't agree with anything the regime is doing ... we are here to serve the Libyan people," he told Al Jazeera.

Dabbashi urged the international community to impose a no-fly zone over Libya to prevent mercenaries, weapons and other supplies from reaching Gaddafi and his security forces.

He said the Libyan diplomats were urging the International Criminal Court, the Netherlands-based body, to investigate possible crimes against humanity in the Libyan context.

Arab League to meet

Hamad bin Jassim bin Jabr Al-Thani, Qatar's prime minister and foreign minister, called for an extraordinary meeting of the Arab League to take place on Tuesday. The aim is to discuss the current crisis in Libya and to put additional "pressure" on the government, he told Al Jazeera.

Hamad bin Jassim said the international community must act now. "I feel a big sympathy for the Libyan people. We don't accept using force in this way or any way against the people or against any nation from their governments," he said.

"And we make our declaration in this space and we think that the international community should also take a stand against what is happening in Libya at the moment."

"I think the [UN] Security Council has to play a role. The condemnation is not enough ... I think the five permanent members and others, they should take the responsibility and do something to help the civillian people in Libya, because what is happening is not acceptable in any way."

Earlier in on Monday, Ahmed Elgazir, a human-rights researcher at the Libyan News Centre (LNC) in Geneva, Switzerland, told Al Jazeera that security forces were "massacring" protesters in Tripoli.

Elgazir said the LNC received a call for help from a woman "witnessing the massacre in progress who called on a satellite phone".

Earlier, a privately run local newspaper reported that the Libyan justice minister had resigned over the use of deadly force against protesters.

Speaking to Al Jazeera, Ahmad Jibreel, a Libyan diplomat, confirmed that the justice minister, Mustapha Abdul Jalil, had sided with the protesters.

"I was speaking to the minister of justice just a few minutes ago ... he told me personally, he told me he had joined the supporters. He is trying to organise good things in all cities," he said.

Jibreel further said that key cities near Libya's border with Egypt were now in the hands of protesters, which he said would enable the foreign media to enter the country.

"Gaddafi's guards started shooting people in the second day ... when they killed two people, we had more than 5,000 at their funeral, and when they killed 15 people the next day, we had more than 50,000 the following day," he said, adding "the more Gaddafi kills people, the more people go into the streets."

Pilots defect

In another development on Monday, two Libyan air force jets landed in Malta and their pilots asked for political asylum, according to a military source.

The pilots, who made an unauthorised landing in Malta, claimed to have defected after failing to follow orders to attack civilians protesting in Benghazi in Libya, Karl Stagno-Navarra, an Al Jazeera contributor, said from Valletta.

The  pilots, who claimed to be colonels in the Libyan air force, were being questioned by authorities in an attempt to verify their identities.

The two Mirage jets landed at Malta's international airport shortly after two civilian helicopters landed carrying seven people who said they were French. Only one of the passengers had a passport.