Nearly 300 people are reported to have been killed in continuing violence in the capital and across the North African country as demonstrations enter their second week.

Navi Pillay, the UN high commissioner for human rights, has warned that the widespread attacks against civilians "amount to crimes against humanity", and called for an international investigation in possible human rights violations.

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Witnesses in Tripoli told Al Jazeera that fighter jets had bombed portions of the city in fresh attacks on Monday night. The bombing focused on ammunition depots and control centres around the capital.

Helicopter gunships were also used, they said, to fire on the streets in order to scare demonstrators away.

Several witnesses said that "mercenaries" were firing on civilians in the city, while pro-Gaddafi forces warned people not to leave their homes via loudspeakers mounted on cars.

Residents of the Tajura neighbourhood, east of Tripoli, said that dead bodies are still lying on the streets from earlier violence. At least 61 people were killed in the capital on Monday, witnesses told Al Jazeeera.

'Indiscriminate bombing'

Protests in the oil-rich African country, which Gaddafi has ruled for 41 years, began on February 14, but picked up momentum after a brutal government crackdown following a "Day of Rage" on February 17. Demonstrators say they have now taken control of several important towns, including the city of Benghazi, which saw days of bloody clashes between protesters and government forces.

There has been a heavy government crackdown on protests, however, and demonstrators at a huge anti-government march in the capital on Monday afternoon said they came under attack from fighter jets and security forces using live ammunition.

"What we are witnessing today is unimaginable. Warplanes and helicopters are indiscriminately bombing one area after another. There are many, many dead," Adel Mohamed Saleh said in a live broadcast.

"Anyone who moves, even if they are in their car, they will hit you."

Ali al-Essawi, who resigned as Libyan ambassador to India, also told Al Jazeera on Tuesday that fighter jets had been used by the government to bomb civilians.

He said live fire was being used against protesters, and that foreigners had been hired to fight on behalf of the government. The former ambassador called the violence "a massacre", and called on the UN to block Libyan airspace in order to "protect the people".

'Genocide'

The country's state broadcaster quoted Saif al-Islam Gaddafi, the son of the Libyan leader, and widely seen as his political heir, as saying that armed forces had "bombarded arms depots situated far from populated areas". He denied that air strikes had taken place in Tripoli and Benghazi.

The government says that it is battling "dens of terrorists".

Earlier, Ibrahim Dabbashi, Libya's deputy ambassador to the United Nations, said Gaddafi had started a "genocide against the Libyan people".

During Monday's protests, gunfire was heard across the capital, with protesters seen attacking police stations and government buildings, including the offices of the state broadcaster.

Witnesses told the AFP news agency that there had been a "massacre" in Tajura district, with gunmen seen firing "indiscriminately".

In Fashlum district, helicopters were seen landing with what witnesses described as "mercenaries" disembarking and attacking those on the street.

Mohammed Abdul-Malek, a London-based opposition activist who has been in touch with residents, said that snipers have taken positions on roofs in an apparent bid to stop people joining the protests.

Several witnesses who spoke to the Associated Press news agency said that pro-Gaddafi gunmen were firing from moving cars at both people and buildings.

State television on Tuesday dismissed allegations that security forces were killing protesters as "lies and rumours".

Benghazi situation dire

Benghazi, Libya's second city, which had been the focal point of violence in recent days, has now been taken over by anti-government protesters, after military units deserted their posts and joined the demonstrators.

Doctors there, however, say that they are running short of medical supplies.

Dr Ahmed, at the city's main hospital, told Al Jazeera that they were running short of medical supplies, medication and blood.

He said that the violence in Benghazi had left "bodies that are divided in three, four parts. Only legs, and only hands,".

While no casualties had been reported in the city on Tuesday, he estimated the number of people killed in Benghazi alone over the last five days to be near 300.

He also said that when military forces who had defected from Gaddafi's government entered an army base, they found evidence of soldiers having been executed, reportedly for refusing to fire on civilians.

The runway at the city's airport has been destroyed, according to the Egyptian foreign minister, and planes can therefore not land there.

Possible 'crimes against humanity'

According to the Paris-based International Federation for Human Rights (IFHR), protesters are also in control of Sirte, Tobruk in the east, as well as Misrata, Khoms, Tarhounah, Zenten, Al-Zawiya and Zouara.

On Sunday, the US-based rights group Human Rights Watch said that at least 233 people were killed in the violence. Added to that are at least 61 people who died on Monday, which brings the toll since violence began on February 17 to at least 294.

Pillay, the UN's human rights chief, called on Tuesday for an international investigation into the violence in the country, saying that it was possible that "crimes against humanity" had been perpetrated by the Libyan government.

In a statement, Pillay called for an immediate halt to human rights violations, and denounced the use of machine guns, snipers and military warplanes against civilians.

Evacuations

Meanwhile, Royal Dutch Shell, a major oil company, said on Tuesday that all of its expatriate employees and their dependents living in Libya have now been relocated.

Emirates airlines and British Airways suspended all flights to Tripoli on Tuesday, citing the violence in the country, even as Italy, France, Turkey, Greece and several other countries were preparing to send aircraft to evacuate their nationals from the country.

Two Turkish ships that were sent to evacuate citizens were not allowed to dock at Tripoli, and one of them then sailed to Benghazi in an attempt to dock there, Anita McNaught, Al Jazeera's correspondent in Istanbul, reported.  

Credit ratings agency Standard & Poor's became the second agency in as many days to downgrade Libya on Tuesday, as it cut the country's rating from A- to BBB+.