They say that the Chinook helicopter had just landed in the easternprovince of Kunar and was off-loading when it was hit through its cargobay.
The attack by the Taliban killed an Afghan interpreter and wounded seven Nato soldiers and an Afghan policeman.
Correspondents say that an attack such as this is rare in Afghanistan.
It is certain to raise questions about security at the Kunar base.
A Nato statement said the landing site had now been secured by troops.
There were about 26 people on board at the time of the attack.
