Twenty-nine civilians, including eight children, were killed in several missile strikes by Israeli drones in Gaza in December and January, according to a report released on Tuesday by Human Rights Watch. The group questioned whether Israeli forces had taken “all feasible precautions” to avoid civilian casualties.

Lt. Col. Avital Leibovich, a spokeswoman for the Israeli military, said Israeli forces had gone to extraordinary lengths to warn civilians during the Gaza offensive, and she questioned the credibility of some of the Palestinian witnesses cited by the advocacy group.

The report represented the latest in a series of accusations of civilian abuse in the Gaza war. And it raised broader concerns about how carefully the remote-controlled drones are being used, much like the complaints that the Central Intelligence Agency has encountered in its use of drones to attack members of the Taliban and Al Qaeda in Pakistan.

The report was partly written by Marc Garlasco, the senior military analyst at Human Rights Watch who was a weapons-targeting official at the Pentagon from 1997 to 2003.

Mr. Garlasco has praised the American military’s use of drones in Iraq and Afghanistan, saying that their ability to hover over a target for many hours had improved the accuracy of many missile attacks and limited civilian casualties.

The group’s findings in Gaza suggest that “the weapon itself isn’t the problem,” he said in an interview. “It’s the way it’s used that is.”

He added: “The operators have the ability to distinguish between combatants and civilians and can even divert the missiles after launch. So it’s hard to understand how the Israelis did such a poor job of targeting.”

Mr. Garlasco said the report, which was released at a news conference in Jerusalem on Tuesday morning, was based on interviews with witnesses to six drone attacks and an examination of debris that suggested a standard drone-fired missile had been used.

The report said one missile had hit a group of university students who were waiting for a bus in the center of Gaza City, while another struck a truck hauling oxygen tanks, and a third smashed into a school sheltering people who had lost or left their homes.

In three other attacks, the report said, the victims were six children, ranging in age from 10 to 15, who were playing on rooftops in residential neighborhoods. Six other children were wounded. Muhammad al-Habbash, the father of one of the girls who was killed, told the human rights group that some of the children were feeding chickens that the family kept on the roof when the missile struck. At another house, Nahla ’Allaw said her son’s legs were crushed and blood poured from small holes in his chest as he died.

While fighters from Hamas, the militant Palestinian faction that controls Gaza, often placed artillery spotters on rooftops, these drone attacks took place early in the conflict before Israeli forces approached Gaza City’s central neighborhoods, the report said.

When asked about the rooftop attacks, Colonel Leibovich, the Israeli military spokeswoman, said, “This is the first time I am hearing of these specific incidents.”

The report said the attacks were a subset of the 42 drone strikes reported by Palestinian organizations, which estimated that as many as 87 civilians had been killed in them.

Israel has said that over all, 1,166 people were killed in the Gaza offensive. Of those, 295 were noncombatants, 709 were Hamas fighters and 162 were men whose affiliations could not be identified, Israeli officials have said.

Colonel Leibovich said Israel did not calculate how many people were killed by different weapons systems, like drones.

After the drone attack on the truck, the Israel Defense Forces released videotape contending that it had killed men who were loading rockets. The military later acknowledged that the cylinders on the truck were oxygen tanks. But the Israeli military still maintains that four of the men who were killed in the incident were Hamas operatives, an assertion that their families deny, the Human Rights Watch report said.

Colonel Leibovich said few military forces had ever taken as many precautions to minimize civilian casualties as Israel did in Gaza, dropping 500,000 leaflets warning people that its forces were arriving and even making telephone calls to neighbors of suspected Hamas fighters.

During the fighting in Gaza, “there were also numerous cases where pilots had to reverse the missiles because they saw civilians enter the area,” she said.

P. W. Singer, the author of a recent book on military robots called “Wired for War,” said Israel may also be finding that using the drones “certainly raises the bar of expectations.”

“Because you can target more precisely, people hold you to a higher standard,” he said.