A large explosion rocked the Afghan capital Kabul today, apparently coming from the direction of the airport, the International Security Assistance Force (ISAF) said.
"We have sent out a team to investigate and to talk to nearby residents," said ISAF spokesman Major Steve Odell.
He said the blast happened at 4.30 a.m. (1 a.m. Irish time) and described it as "unexpected."
"At this altitude, sound travels long distances and it is difficult to say what happened or where," he said.
"We have no more information."
There were two further blasts about three hours later, believed to be in the city limits, which Mr Odell said were believed to be the deliberate destruction of unexploded ordnance.
Kabul is littered with land mines and other debris of 23 years of war and there are occasional rocket attacks, but the old weapons, apparently fired at random, usually fail to go off.
One landed a few hundred yards from the Reuters office last week.
The ISAF has been responsible for security in Kabul since shortly after the former ruling Taliban were forced from power late last year.