BAGHDAD, Iraq — Five American soldiers and an Iraqi civilian were killed in a suicide bombing while chatting with shopkeepers in central Baghdad on yesterday, part of an uptick in high-profile attacks that has rattled the capital after months of diminished violence. At least three more suicide bombings took place across the nation yesterday, including an attack on a hotel in the comparatively peaceful Kurdish north that killed two people and injured 31. Such attacks are a hallmark of Sunni Arab militants loyal to Al Qaeda in Iraq, a mostly homegrown insurgent group that American commanders say is led by foreigners.

American officers concede that some of the recent attacks have caused significant loss of life but say it is too soon to declare a reversal of the progress in recent months.

U.S. Navy Rear Adm. Gregory Smith told reporters Sunday that the number of attacks remains far lower than a year ago.

“I would not look at the last few weeks as an increase or a trend,” he said. “That said, on any given day, Al Qaeda and other extremist groups are still very much disposed toward handing out violence indiscriminately. … We have every expectation that there will be bad days to come in the future.”

A rise in violence would raise questions about American plans to pull out most of the 28,500 additional troops deployed last year, bringing the force level down to about 140,000. Two brigades have left since December without being replaced, and another three are scheduled to rotate out by the end of July.

Commanders here have said they will need time to assess the feasibility of additional cuts. General Petraeus will present his recommendations to Congress next month.

Yesterday’s bombing was the worst single attack on American forces in the capital since June, the month that the buildup was completed.

Iraqi police said a man with explosives strapped to his waist walked up to soldiers on foot patrol in the upscale Mansour neighborhood and blew himself up. An American military statement confirmed that initial reports indicated a suicide vest was used.

The blast also injured three American soldiers, their Iraqi interpreter, and nine other Iraqis, including a soldier and a policemen, American and Iraqi officials said.

Neighborhood grocer Razaq Jawdat said the American patrol, accompanied by Iraqi troops and policemen, had stopped near his store to chat with local merchants.

“Suddenly a suicide bomber with a vest came up and blew himself up,” Mr. Jawdat said from a hospital bed, where he was being treated for shrapnel wounds. “I saw with my own eyes three dead American soldiers.”

It was the deadliest attack on American troops in Iraq since January 28, when five soldiers were killed in a roadside bombing followed by a gunfight in the northern city of Mosul. The last time that many American troops were killed in a single incident in Baghdad was June 28, an attack that also involved a roadside bomb, gun, and grenade fire.