The bomb exploded on Tuesday in Maimana town, the provincial capital of Faryab, minutes after an explosion outside a Western-funded aid group called Coordination of Humanitarian Assistance (CHA), the officer said.

The first blast caused minor damage to the CHA office, but attracted a crowd of people to the site.

“While police and civilians gathered to see what had happened a second explosion occurred,” said Faryab’s governor Abdul Latif.

The wounded included two soldiers from the Afghan National Army, a policeman and one civilian, said Mohammad Aslam, a senior police officer for Maimana town.

Latif said no arrests had been made and the bombs were probably detonated by remote control.

He blamed terrorists, a term usually used by Afghan officials to describe members of the ousted Taleban militia and their al Qaeda allies.

Two CHA workers were killed in the southern province of Kandahar in April last year in an attack blamed on the Taleban.

Islamist militants are mostly active in the restive south and east, where they have been waging an insurgency since the US-led forces toppled the Taleban from power in 2001.

But a handful of aid groups and foreign workers have come under attack in northern provinces. Eleven Chinese engineers were killed in the northeastern province of Kunduz last June.