Tripoli, Libya (CNN) -- The nightmare in Libya's war-torn city of Misrata intensified Monday amid more shelling on the city and desperate measures to get medical care, an opposition spokesman said.

"The aid coming from outside is not enough. There is no hospital," said the spokesman, who wanted to be identified only as "Mohammed" for safety reasons.

He said 21 people were killed and more than 100 were injured from shelling Sunday in Misrata. Monday's shelling fell on the city's critical port area -- Misrata's lifeline to humanitarian aid -- and an industrial area that includes small businesses and small factories.

With a city hospital taken over by pro-government forces, makeshift clinics have popped up to treat the wounded. And in a city where access to food, water and electricity has been scarce, Mohammed said people have been using cell phones for light during surgery.

"(With) all of this happening, we haven't seen NATO," Mohammed said, referring to the alliance that has led airstrikes against Libyan ruler Moammar Gadhafi's military resources. "There have been no strike for four days in Misrata."

As the battle between pro-Gadhafi forces and rebels demanding an end to Gadhafi's four-decade rule forges ahead, a United Nations official said Monday that her meeting with Gadhafi regime members did not end with a promise to stop attacks.

Valerie Amos, U.N. under-secretary-general for humanitarian affairs and emergency relief coordinator, spoke to reporters Monday in the Libyan rebel stronghold of Benghazi. She said she visited Gadhafi regime officials in Tripoli on Sunday.

"Let me be absolutely clear. I got no guarantees with respect to my call for the overall cessation of hostilities to enable people to move, to enable us to deliver supplies," Amos said. "I did get an assurance from the government to carry out a needs assessment in Misrata."

She added, "I have to say in that instance we got no guarantees at all that the violence would cease."

Britain will help 5,000 people trapped in Misrata "escape the besieged city and will provide vital medical assistance to those who remain in towns across western Libya," the UK Mission to the United Nations announced Monday. The evacuations "will get foreign workers who have managed to reach Misrata's port safely out of the town," the mission said in a statement.

Meanwhile, a British official is expected to meet with U.N. leaders Monday to discuss the humanitarian crisis in Libya.

"Agencies working inside (Misrata) report shortages of critical supplies and attacks targeted against civilians and medical facilities," according to a statement from the UK's Department for International Development. The statement said International Development Secretary Andrew Mitchell will travel to the United Nations for "urgent talks" Monday.

Misrata isn't the only city deluged by violence.

On Sunday, forces loyal to Gadhafi shelled the city of Ajdabiya from 40-50 kilometers (25-31 miles) away, Libyan rebel spokesman Shamsiddin Abdulmolah told CNN. The loyalists who were targeting the city "have no problem with the weather conditions there," referring to unconfirmed reports that NATO airstrikes were halted in the area due to weather conditions.

Gadhafi's forces were using missiles and mortars, "and sometimes we feel that NATO wants to use any excuse out there so they don't carry out their duties," Abdulmolah said.

"We can't understand (NATO's) excuses. We want to save our population from being murdered by (Gadhafi's) merciless death squads," he added.

NATO did not immediately respond to a CNN inquiry about its operations Sunday.

Earlier, however, the NATO press office told CNN that it does not discuss ongoing operations and would not confirm or deny any reports. An official report from NATO stated the alliance conducted 142 sorties on Saturday, of which 42 were strike sorties.

NATO is operating under a U.N. Security Council resolution authorizing the use of force to protect Libyan civilians. The alliance has said Gadhafi's forces started hiding resources in civilian areas, making airstrikes much more difficult to carry out without harming civilians.

Misrata remained in control of the rebels on Sunday, Abdulmolah said, though they were fighting about 200 to 300 Gadhafi troops inside the city.

Rebel fighters pushed back Gadhafi's squads to a shoe factory, from where they were shelling residential areas in the city, he said. NATO refused to bomb the shoe factory because it is a civilian facility, he said. In the end, the rebels pushed the loyalists out of the shoe factory, which they burned.

Despite the incessant struggle, Abdulmolah said he was optimistic the rebels could overcome Gadhafi's forces.

"We are confident that we will be able to liberate the city completely and rescue our civilians who are being targeted by the madness of Gadhafi's death squads," he said. CNN's Reza Sayah, Yousuf Basil, Frederik Pleitgen, Saad Abedine, Salma Abdelaziz, Mitra Mobasherat and Bharati Naik contributed to this report.

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