A suicide bomber attacked an Afghan army bus in Kabul on Sunday, killing four people and wounding up to 22, police said, the latest incident in a worrying surge of violence in the Afghan capital over the past 10 days.
The Taliban quickly claimed responsibility for the attack, the worst since a devastating assault on a popular restaurant on January 17 killed 21 foreigners and Afghans.
Hashmat Stanikzai, the chief spokesman for police in Kabul, said an investigation into the latest attack was under way.
"The number (of victims) might change," he said.
Stanikzai said the wounded included children who were nearby when the blast occurred.
The Afghan capital was hit by at least two other attacks in the previous 24 hours, according to security officials.
Two people were wounded in an explosion in the north of the city late on Saturday, while security sources said a rocket landed near the international airport on Kabul's outskirts without causing casualties.
The restaurant attack on January 17 was the worst on foreigners since the Taliban were overthrown by U.S.-led Afghan forces in late 2001 and sent shockwaves through Kabul.
Three United Nations staff and the International Monetary Fund's top representative in Afghanistan were among the 13 foreigners killed in that attack.