The biggest casualty toll was in southern Kandahar, where a car bomb killed seven adults and eight children, CNN said. Officials said the district where the explosion happened is politically unstable and has a heavy presence of fundamentalist Taliban fighters.
In the eastern province of Khost, a police commander and two others were killed and 12 people injured in a suicide attack, officials said.
The Ministry of Interior said a mortar attack in the eastern province of Kunar killed six civilians, including two children.
The news emerged as the United Nations released a report saying May had the highest number of civilian violence-related deaths since 2007. It said 368 civilians were killed in May, 45 of which were blamed on Afghan and NATO-led forces.
Georgette Gagnon, the director of human rights for the U.N. Assistance Mission in Afghanistan, said in a statement the upward trend is alarming.
"We are very concerned that civilian suffering will increase even more over the summer fighting season which historically brings the highest numbers of civilian casualties," Gagnon said.