Extra police and troops have been marshalled across Afghanistan after the Taliban announced a stepped-up campaign of violence.
Within hours of the hardline Islamists beginning their annual spring offensive, their bombs and bullets killed at least 11 people.
Taliban leaders have warned civilians to stay away from public gatherings, military bases and convoys, as well as government offices.
In Paktika, a dangerous province in the southeast near the border with Pakistan, a suicide bomber wearing an explosives-packed vest blew up himself, killing four civilians and wounding 12.
A statement from the Paktika governor's office said the bomber was 12-years-old.
In central Ghazni city, two police and two civilians were killed in a gunfight after insurgents opened fire on a passing police vehicle, the police chief said.
Also in Ghazni, a bomb planted on a bicycle went off near the police headquarters, wounding 13 civilians, a hospital official said.
The governor of Kandahar province, the birthplace of the Taliban, ordered thousands of security forces onto high alert, with police and Afghan soldiers manning checkpoints on every roundabout in Kandahar city.
Gunmen on a motorbike killed an Afghan soldier in Kandahar.
In Logar, south of Kabul, two members of a community police unit were killed by a roadside bomb, police officials said.
Senior military commanders have been expecting a spike in violence with the arrival of the spring and summer "fighting season", although the usual winter lull was not seen as US-led forces pressed their attacks against insurgents, particularly in the Taliban's southern heartland.
Senior military officials say recent intelligence reports indicate the fresh campaign of increased violence will last about a week and be mounted by the Taliban, supported by the al Qaeda-linked Haqqani network and other insurgents.