Rebels said they fought fierce clashes with pro-government troops in the Libyan city of Misrata on Wednesday and medical workers said five civilians were killed in mortar attacks.
Eight people had been killed on Tuesday, mostly civilians, according to rebels.
Libya's third-largest city, the insurgents' last major stronghold in the west of the country, has been under siege for more than seven weeks in a civil war that erupted in February.
Hundreds of people are believed to have been killed in the city of 300,000, where aid groups say the humanitarian situation is worsening with a lack of food and medical supplies.
In a sign of the hardship, this correspondent saw a long queue for petrol. Electricity has been cut in the city so residents depend on generators.
There were several checkpoints on the rebel-controlled route from Misrata's port towards the centre. A man armed with a hunting rifle stood at one of the checkpoints.
Thousands of stranded foreign migrant workers are awaiting rescue in Misrata's port area.
"Fierce fighting is taking place now on the Nakl el Thequeel road which leads to the port. Gaddafi forces have been trying to control this road to isolate the city," Abdelsalam, a rebel spokesman, said earlier.
"NATO warplanes are flying over Misrata but I do not know if there are strikes," he said by phone from the city. "NATO has been inefficient in Misrata. NATO has completely failed to change things on the ground."
He said "violent fighting" had also erupted on Tripoli Street, a main thoroughfare and another key battleground, in the morning. "I'm hearing explosions now. A large number of snipers are positioned there," Abdelsalam said. "Civilians can not come out for fear of being shot dead."
Libyan officials say they are fighting militia with ties to Al-Qaida bent on destroying the oil-producing North African state. They deny that government troops are shelling Misrata and its civilians.
The insurgents' claims of gains on the ground in recent days -- despite heavy shelling by government forces at times -- have not been verified independently.
The rebels "are now controlling 50 percent of the street. The other 50 percent is controlled by Gaddafi soldiers and snipers," another rebel spokesman, Reda, said, referring to Tripoli Street. Like Abdelsalam, he only gave his first name.
Reda said the area near the city's port -- an insurgent-held zone that is a lifeline for trapped civilians and for badly needed food and medical supplies -- was calm on Wednesday morning and ships were able to dock.
"A Turkish ship carrying humanitarian aid arrived there about 30 minutes ago. Two Qatari ships were in yesterday. They evacuated around 1,500 Africans," Reda said, referring to migrant workers desperately trying to flee Misrata.
A ship bringing humanitarian aid to Misrata arrived in the port on Wednesday aiming to evacuate more stranded migrants, estimated to number around 5,000 in the port area.
"We don't know whether we will be able to reach them, however," Jeremy Haslam of the International Organisation for Migration (IOM) said in a statement. "If they are not close to the port, then it will be extremely hard to access them given the security conditions in the city."
The Geneva-based aid agency -- which said it had evacuated 2,100 people from Misrata in two earlier such missions -- said the Ionian Spirit ship carried 500 tons of food, medical supplies, and other aid as well as a team of 13 doctors.
In New York, UN humanitarian chief Valerie Amos said Libyan officials she spoke to in Tripoli last weekend promised to ensure the security of aid workers trying to get to Misrata.
"So we will try to get to Misrata by road as well as trying to get in by sea," she told reporters.
Amos, who said she would send a team to Tripoli next weekend following an agreement she signed to set up a presence in the Libyan capital, repeated that her department did not at present need a military escort offered by the European Union.
But she said that if civilian means of getting in aid became impossible, "we would have the opportunity to call on them for support from military assets."
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