BAGHDAD — A suicide bomber slammed his truck into a densely populated residential area in the northern Iraqi city of Tal Afar today, killing at least 28 people, including 19 children, local authorities said.

The attack occurred in a crowded Shiite neighborhood of the religiously mixed city, 260 miles northwest of Baghdad.

The powerful blast caused houses to collapse in the morning as many families were getting ready for the day ahead, and officials said the death toll could rise.

"Rescue teams are still searching for casualties among the rubble," said Ali Abbo, the head of the human rights committee.

He said the hospital in Tal Afar had been filled to capacity, forcing the ambulances to take many victims to Dahuk, about 45 miles to the north.

At least 40 others were wounded in the attack, said Brig. Gen. Rahim al-Jibouri, commander of Tal Afar police.

The attacker drove a dump truck filled with explosives and covered with a layer of gravel, Brig. Gen. Najim Abdullah said, adding that at least 19 children were among the 28 killed.

Within an hour of the attack, authorities imposed a complete curfew on the city, he said.

The United States and Iran, meanwhile, held expert-level talks on security issues in Baghdad, more than two weeks after the ambassadors of both arch-enemies agreed to establish a committee to discuss efforts to stabilize Iraq.

The American delegation was led by the U.S. Embassy's counselor for political and military affairs, Marcie B. Ries, embassy spokesman Lou Fintor said.

Iraqi President Jalal Talabani hosted the sides, who sat at three separate conference tables in an Iraqi government office.

"His excellency expressed hope that the long-awaited Iranian-Iraqi-American meeting will succeed in achieving security and stability in Iraq," Talabani's office said in a statement. "The president hopes that Iran will play a positive role in finding a way to achieve the ambitions of the Iraqi people."

The talks come as the U.S. military steps up accusations that Tehran is arming and training Shiite militants to attack American forces.

Lt. Gen. Raymond Odierno, the U.S. second-in-command, said Sunday that rogue Shiite militiamen with Iranian weapons and training launched 73 percent of the attacks that killed or wounded American forces last month in Baghdad, nearly double the figure six months earlier.

Tal Afar also recorded one of the deadliest days since the start of the Iraq war, when at least 152 people died in truck bombings on March 27. That attack prompted Shiite militants and police to go on a shooting rampage against Sunnis, killing as many as 70 men execution-style.