The military's assault on the city, a linchpin of the five-month-old uprising against the iron-handed government of President Bashar al-Assad, represents one of the fiercest efforts yet to crush the uprising and a signal of Mr. Assad's defiance in the face of growing international condemnation. Activists say the overall toll from the repression since March is more than 1,700.

With foreign journalists barred from the country and the government silent about most aspects of the rebellions, activists have been the main source of information on the crackdowns and casualties.

Landlines, cellphones, Internet service, electricity and water remained cut for the second consecutive day in Hama. Satellite connections offered perhaps the only route left to get information out. Activists said they feared the near total media blackout on the city would allow the military to pursue an unrestrained assault. Their fear was deepened by the painful legacy of Hama, where Mr. Assad's father Hafez, president at the time, crushed an uprising in 1982 out of sight of the world, leaving upwards of 10,000 people dead and parts of the city leveled.

Other activists spoke of a critical shortage in basic food staples and medical equipment. Hama has been surrounded since Sunday, and cars trying to carry food into the city have been attacked, according to reports in recent days. Hundreds of people have been arrested in house-to-house raids.

Saleh al-Hamawi, an activist with the Local Coordination Committee which helps organize and document protests, said via satellite phone from Hama that armed forces started shelling the city in the early hours of Thursday and that it has been sporadic since then.

"We are facing a food and medical equipment crisis," said Mr. Hamawi. "We don't have flour, or vegetables. People are borrowing food from their neighbors."

A Thursday morning post on the official Syrian Revolution Facebook page said that heavy gunfire could be heard across the city and that armed men loyal to the government had occupied private hospitals and snipers took positions on their rooftops. It also said that hospitals were suffering from shortages of basic supplies including fuel for generators, a crucial backup for electricity.

Six people were also reported killed across the country when troops and armed men loyal to the government opened fire at them during evening demonstrations held after special Ramadan prayers.

Activists also said that at least 1,000 families had fled Hama since Sunday.

Syria's state-run media has conspicuously avoided mention of the Hama siege, focusing instead on news that suggests normalcy in the country and what it has described as Mr. Assad's noble attempts to promote political dialogue and openness. The top story Thursday on the English-language web site of SANA, the official news agency, was about Mr. Assad's endorsement of a draft law allowing multiple political parties. Syria's political opposition denounced the law as a joke when it was first announced last month.

Mr. Assad's endorsement of the law only seemed to add to the international outrage over the repression. France called it a "provocation."

In a further sign of Mr. Assad's deepening isolation abroad, the president of Russia — a close Syria ally — criticized him in unusually blunt terms. The criticism by President Dmitri A. Medvedev, in an interview with Russia radio and television from the southern Russia resort of Sochi, came a day after Russia joined with other members of the Security Council in rebuking Mr. Assad for the repression.

"He needs to urgently carry out reforms, reconcile with the opposition, restore peace and set up a modern state," Mr. Medvedev said. "If he fails to do this, he will face a sad fate."

Rick Gladstone contributed reporting from New York.