Story highlights It was not clear if the wounded US citizen was a military service member or a contractor

The Taliban claimed the attack was carried out as revenge for leaflets distributed by US-led NATO forces in the area on Tuesday

Washington (CNN) A US citizen was wounded Wednesday following an apparent suicide attack at an entrance gate to Bagram Air Base in northern Afghanistan, US military officials tell CNN.

According to the officials, the attacker was riding a motorcycle and did not make it past any checkpoints.

Bagram District Governor Abdul Shukoor Qudosi told CNN the attacker detonated his explosives at the main entrance of the base, targeting truck suppliers.

It was not clear if the wounded US citizen was a military servicemember or a contractor.

"The explosion resulted in a small number of casualties. The casualties are being treated at Bagram medical facilities," US Forces Afghanistan said in a statement. The statement also said: "Bagram Airfield is secure and the incident is being investigated."

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