Attackers set off a car bomb near the office of the Save the Children aid agency in the eastern Afghan city of Jalalabad on Wednesday and then clashed with security forces, a provincial government spokesman said.
"There was a blast and the target was Save the Children," said the spokesman, Attaullah Khogyani. A clash was going on after the blast, he said.
Khogyani had no word on casualties but the director of the provincial health department said 11 wounded people had been taken to hospital.
There was no immediate claim of responsibility.
There were several other aid groups and government offices in the immediate area, raising the possibility that Save the Children was not the target.
Jalalabad is the capital of Nangarhar province, on the porous border with Pakistan.
The province has become a stronghold for Islamic State, which has grown to become one of Afghanistan's most dangerous militant groups since it appeared around the beginning of 2015.
Backed by intensive U.S. air strikes, Afghan forces have claimed growing success against the Taliban and other militant groups, including Islamic State, but attacks on civilian targets have continued, causing heavy casualties.
The attack in Jalalabad came just days after Taliban militants attacked the Hotel Intercontinental in the capital, Kabul, killing at least 20 people, including 13 foreigners.