The Taliban have claimed responsibility for an overnight attack in Afghanistan that killed four US troops and wounded six other, just hours after Washington said its officials would meet the insurgents for talks.

US President Barack Obama earlier welcomed the planned talks as " important first step " but warned of a long and bumpy road ahead as Afghan and NATO troops continue to battle a 12 - year insurgency.

" Last night two big rockets were launched at Bagram(air base) which hit the target. Four soldiers are dead and six others are wounded. The rockets caused a major fire, " Taliban spokesman Zabihullah Mujahid said on Wednesday.

Bagram is the biggest US - led military base in Afghanistan and lies just north of the capital.

The Taliban broke off contact with the Americans last year and have always refused to negotiate with Kabul, but on Wednesday they unveiled an office in Qatar " to open dialogue between the Taliban and the world. "

Their statement, however, made no direct reference to peace talks.

Wednesday also saw NATO ' s formal transfer of responsibility for security to the Afghan police and army. About 100,000 international combat troops, 68,000 of them from the US, are due to withdraw by the end of next year.