Casualties were feared as an explosion shocked eastern Afghanistan's Parwan province on Saturday, a security source said.

"A powerful explosion occurred in Du-Saraka locality, Bagram District of eastern Parwan province. The blast took place at around 9:00 a.m. local time (0430 GMT), and the nature of the explosion was not known so far," the source told Xinhua anonymously.

A main US and NATO forces' military base is located in the district in the province, 65 km north of Afghan capital of Kabul.

"We still cannot provide details on causalities. There is fear of possible causalities. An investigation was underway and details will be revealed to public later on the day," the source noted.

Unofficial sources said that target of the attack was a NATO- led forces' military convoy running on a main road in the area.

Government troops cordoned off the area shortly after the blast, keeping people from gathering at the scene for fears that there might be a second blast.

No group has claimed responsibility for the attack yet.