Heavy artillery shells continued to fall on cities in Syria on Wednesday, despite the presence of U.N. observers charged with monitoring a nominal cease-fire in the country, residents said.

In the central city of Hama, where two monitors are stationed, activists said as many as 70 people were killed when soldiers shelled a poor residential area, causing buildings to collapse and crush families.

“We are under fire right now,” said an opponent of President Bashar al-Assad who lives in the Douma suburb east of Damascus, where anti-government demonstrations are common and heavy fighting has broken out in the past six months.

The activist, who uses the pseudonym Adam Nasir, said U.N. observers came to Douma on Wednesday after an initial visit Monday, when they were mobbed by people eager to tell them about the months-long military crackdown and waves of arrests in the area.

“I met them myself,” he said. “I told them everything about the humanitarian situation, the martyrs, the injured, everything we had.” But on Tuesday, government forces began using heavy weapons in Douma again, Nasir said, defying a clause in the cease-fire agreement worked out by special envoy Kofi Annan and endorsed by Assad that requires a halt to shelling in urban areas.

On Wednesday, Nasir said, the observers who had returned to Douma fled when shooting resumed. “These observers, how do they help us?” he said. “The regime doesn’t care about the observers.”

Speaking to the U.N. Security Council on Tuesday, Annan emphasized concerns that people in Hama, where dozens of civilians were reportedly killed Monday, had been targeted after opposition leaders spoke to U.N. monitors over the weekend. Independent confirmation of death tolls is difficult because of the Syrian government’s restrictions on journalists.

Fewer than 20 monitors are in Syria, and Annan has urged the rapid deployment of the 300 unarmed military personnel who are set to make up the full mission, but the head of U.N. peacekeeping operations, Herve Ladsous, has said that it will take a month for the first 100 members of the contingent to reach the country.

Some officials have expressed alarm at the pace of deployment of a mission that was agreed to in principle at the start of the month, pointing to the ongoing violence.

“This cannot continue indefinitely,” French Foreign Minister Alain Juppe told reporters in Paris on Wednesday.

“We want to see observers in sufficient numbers, at least 300 . . . deployed as quickly as possible.”