KANDAHAR, Afghanistan — At least 16 people, including security personnel and bystanders, were killed on Tuesday as bomb disposal experts tried and failed to defuse explosives in a parked car in the southern city of Kandahar, Afghan officials said.

Daoud Ahmadi, a spokesman for the governor of Kandahar Province, said the car had been parked in an auto repair garage in the center of the city. Four of the 16 people killed were members of the security forces, Mr. Ahmadi said, adding that an additional 38 people were wounded. Most of the casualties were civilians, he said, and some were children.

The Kandahar explosion came a day after the Taliban warned that they were planning attacks on government, police and intelligence facilities in Kabul, the capital, and asked civilians to stay away from such institutions.

The statement included an unsupported claim that the insurgents had brought about an “unprecedented” decrease in civilian casualties. United Nations figures on civilian casualties in Afghanistan show a slight decrease in 2017 from the previous year, but the numbers remained at historically high levels, with two-thirds of them caused by the insurgents.