NATO stepped up airstrikes around the besieged Libyan city of Misurata on Wednesday, destroying 12 government tanks, after criticism from within its own ranks that it was not doing enough to stop the Libyan government from shelling and shooting indiscriminately at civilians in the rebel-held portion of the city.

Rebels, who control Misurata’s port and much of the north and east of the city, reported heavy fighting but said things seemed finally to be going their way.

The situation for civilians, however, remained desperate, and a spokesman for the city council appealed for NATO to send in ground troops to protect civilians and prevent a massacre.

“Every single day, mortar shells and tank shells are falling randomly all around the city,” said the spokesman, who insisted for safety reasons that he be identified only by his first name, Mohammed. “It is endless madness and carnage.”

On Wednesday, The Washington Post received photographs from local doctors of an ambulance hit by a mortar shell just that evening, along with disturbing pictures of three badly wounded and very young children hit by shellfire in their parents’ home and car. Two of the children survived, one doctor said.

“All we can smell is smoke and blood, all we can hear is crying children,” said Aiman Abushahma, a doctor at a Misurata hospital. “We sleep to the sound of shellfire, we wake up to the sound of shellfire. They are shelling ambulances, they are shelling medical staff.”

Misurata, Libya’s third-largest city, lies just 131 miles east of the capital, Tripoli. As the rebels’ only foothold in western Libya, it represents a strategic prize for both sides in the conflict — and a major irritant for Moammar Gaddafi’s forces, who would like to regain control of the city before moving decisively against rebel strongholds far to the east

On Tuesday, the foreign ministers of France and Britain said their NATO partners were not doing enough to help protect rebel-held cities such as Misurata from attacks by Gaddafi’s troops, although NATO commanders say it is often difficult to isolate military targets in urban settings without putting civilians at risk.

Mohammed, the city council spokesman, said that NATO airstrikes had destroyed hundreds of tanks around Misurata and badly disrupted Gaddafi’s supply lines, but that government forces were now hiding tanks and heavy artillery in schools, hostels and hospitals.

With Misurata encircled by government forces for seven weeks, the humanitarian situation in the city is “grave” and deteriorating, said the United Nations children’s agency, UNICEF.

Virtually the entire population of 300,000 of this once bustling commercial city is crammed into just a third of the area, with homes, schools and mosques all full. Water has been cut off for weeks, and sewage systems are disrupted. Electricity is also out in much of the city, and the streets are not safe from snipers and shellfire.

Shahida Azfar, UNICEF’s regional director for the Middle East and North Africa, said more than 20 children had died as a result of shooting and shelling by government forces. “The siege must stop,’’ she said.

More than 260 people, most of them civilians, have been killed in Misurata since the siege began, according to local doctors interviewed via Skype.

The Libyan government denies killing any civilians in the city.

On Monday, Social Affairs Minister Ibrahim al-Sharif said all the children killed were victims of NATO airstrikes. On Tuesday, government spokesman Moussa Ibrahim blamed civilian deaths on “armed gangs” and “al-Qaeda affiliates,” as he refers to the rebels.

Correspondent Leila Fadel in Benghazi, Libya, contributed to this report.