The three, whose nationalities have not been disclosed in line with policy, died when a roadside bomb exploded in the east of the country.

No further details were immediately available of the incident.

More than 500 Nato troops have been killed so far this year in Afghanistan.

Much of the decade-long Afghan conflict's worst fighting takes place in eastern Afghanistan, close to the border with Pakistan.

Pakistan closed its supply routes to Nato forces in Afghanistan after 24 Pakistani soldiers were killed by a Nato air strike last Saturday close to the mountainous, porous border.