The United Nations says it has been guaranteed humanitarian access to Misurata, while Britain says it will fund efforts to evacuate thousands of stranded migrant workers by boat from the besieged port city.
A Libyan official told Valerie Amos, the UN humanitarian chief, that Muammar Gaddafi's government was willing to set up "safe passage" out of the city, which remains partially in opposition hands after weeks of attacks by Gaddafi loyalists.
Amos secured the deal through talks in Tripoli, apparently pledging to up the UN presence in the capital in return for humanitarian access in other Libyan cities.
But she said that while she had received assurances the UN would be able to access the city, she received "no guarantees" of a cessation of hostilities "to enable people to move" or for supplies to be delivered. Witnesses said government forces continued to pound the area with rockets and artillery.
Andrew Mitchell, the UK's international development secretary, said meanwhile that the UK would provide £2m ($3.3m) in aid and work through the International Organisation for Migration (IOM) to charter a ship to get Egyptian and Bangladeshi workers out of Misurata.
Mitchell's comments came in New York, where he discussed the plan with UN agency chiefs.
Speaking on the BBC, he said: "The position in Misrata, which has sharply deteriorated in the last few days, means that there are 5,000 poor migrant workers caught out on the quayside ... we're going to move all of them out as soon as we can by sea."
Ahead of the planned British mission, almost 1,000 people were rescued from Misrata by ferry, but the IOM said that thousands more were awaiting rescue.
"The ship docked in Benghazi straight from Misurata carrying 970 passengers on board," reported Sue Turton, Al Jazeera's correspondent in Benghazi, the rebel stronghold.
"The majority were Ghanaian migrant workers, but it also had some casualities from the fighting, including a young baby girl who has gunshot wounds, we think, to the face."
In Geneva, the International Committee of the Red Cross said it had also helped 618 migrants leave Misurata on Monday.
Many of those who have been rescued are injured. An Associated Press report said that one of the rebels carried fragments of rockets as he disembarked late on Monday.
"I brought this to show people what's going on there [in Misurata]. Somebody has to do something about it," 38-year-old Ali Milad, was quoted as saying.
The Libyan government has denied firing heavy weapons, including rockets and tank shells, at the city, but has turned down repeated requests by foreign journalists based in the capital of Tripoli to go to Misurata.
The rebels control much of eastern Libya, including Benghazi, and have done so since the uprising against Gaddafi began in mid-February.