An Afghan reporter for The New York Times who reached the scene said he saw children as well as men in army uniforms among the victims. “Most of the dead children are shoe polishers working in the area,” he said. “You could see their shoe polish boxes and brushes still there.”

President Hamid Karzai called the suicide bombing a “vile attack” that nonetheless would only encourage more recruits to join the fight against the Taliban. “It will by contrast embolden their resolve and dedication to eliminate a cruel enemy that wants nothing but bloodletting,” he said in a statement.

A spokesman for the Taliban, Zabiullah Mujahid, took responsibility for the attack and said the bomber was a Kunduz resident, whom he identified by his single Afghan name, Saifullah.

“I strongly deny the allegation of civilian casualties in the attack,” Mr. Mujahid said. “Some known, pro-puppet-government circles claim that civilians and children who were playing in an adjacent park are among the dead, but in fact the park is almost a hundred meters away from the blast site.”

He conceded, however, that shoeshine boys were among the victims. “While we are really sorry for any innocent civilians’ losing their lives in our action, we strongly advise civilians not to approach Afghan and foreign military convoys, bases and individuals.”

The shoeshine boys, Mr. Mujahid added, “were in the wrong place at the wrong time.”

In late January, the Kunduz Province police chief, Abdul Rahman Saidkhaili, boasted that Kunduz was, in his words, “100 percent cleared of Taliban.” Ten days later, a suicide bomber killed the governor of Chardara district in the province, jumping on him in his office on Feb. 10.

Image Taliban activity has shifted from Afghanistan’s south to the north. Credit... The New York Times

Then, on Feb. 21, another bomber entered the district government offices in Imam Sahib district, killing 34 people, many of them militiamen waiting to get national ID cards. And on March 10, a suicide bomber jumped on the police chief himself, killing him and three of his companions.