* Humanitarian situation is "catastrophic"
* British PM says Misrata suffering "murderous attacks"
(Adds new quote from rebels, more details)
By Hamid Ould Ahmed
ALGIERS, March 29 (Reuters) - Rebels in the Libyan city of Misrata said they had come under intense attack on Tuesday by forces loyal to Muammar Gaddafi, and appealed to governments meeting in London to help them.
"Gaddafi's forces are launching intensive and vicious military campaigns against us in Misrata," rebel spokesman Mohamed said by satellite telephone. "They are determined to capture the city. Today was tough for the rebels."
Misrata, under siege for several weeks, is the last big rebel stronghold in western Libya. Some Western leaders cite it as proof that foreign military intervention must carry on if it is to protect civilian lives in the Libyan conflict.
Accounts from the city speak of bombardments killing dozens of people, sniper fire from rooftops, and food and water running out.
"The humanitarian situation is catastrophic. There is a shortage of food and medicine. The hospital is no longer able to deal with the situation," rebel spokesman Sami said.
Another rebel spokesman, Saadoun el Misrati, said a total of nine people had been killed on Tuesday. Rebels in the eastern city of Benghazi, their main stronghold, said 124 civilians had been killed in the past nine days in Misrata, a city of 300,000 people.
"Gaddafi's forces went into houses in Zawabi, which is near Tripoli street, and killed four brothers and two of their neighbours," Misrati said. "We are sure they have positioned snipers on the rooftops of these houses."
In London, where more than 40 governments and international bodies met to discuss Libya's future, British Prime Minister David Cameron said: "As I speak, people in Misrata continue to suffer murderous attacks from the regime."
Reports from Misrata, about 200 km (125 miles) east of the capital Tripoli, could not be independently verified because Libyan officials have not allowed journalists to work freely there.
Authorities in Tripoli say the insurgents are Islamist militants holding the population hostage.
The Al Jazeera news channel said that Qatar was sending ships to Misrata to evacuate Egyptians trapped there.
A Libyan doctor based in Britain who said he was in contact with people in Misrata urged Western governments to do more to protect the city's civilians from attack.
"The coalition force should stop this ongoing massacre," he said. "Either they are fully committed to protecting these civilians or should leave them to their destiny."
Western air strikes have targeted an air base near Misrata and some positions held by pro-Gaddafi forces.
Rebel spokesman Mohamed said the planes had bombed pro-government Gaddafi vessels near the port that had tried on Saturday night to land forces in Misrata.
But rebels say government troops have driven heavy armour into the city, making it difficult to hit them from the air. (Additional reporting by Michael Georgy in Tripoli, Joseph Nasr in Berlin and Miriam Karouny in Beirut; Writing by Adam Tanner; Editing by Kevin Liffey)