A suicide bomber targeting a U.S. military convoy detonated a motorbike packed with explosives outside a boys' high school in eastern Afghanistan Monday killing at least 10 students, and two American soldiers.

About 20 people were wounded in the attack -- most were schoolchildren

Concerns are mounting over how Afghan security forces will cope with an intensifying insurgency once most foreign troops leave by the end of next year.

Western officials say the insurgency is responsible for about 86 per cent of all civilian casualties - or about 1,500 people - across the country this year.