The Taliban on Saturday claimed responsibility for a suicide attack on a NATO convoy in the Afghan capital, Kabul.
Reuters reported that at least four people had been killed. The news agency quoted an Afghan interior spokesman as saying three civilians and a police officer had died.
NATO said some of its forces were amongst the dead but the exact number is as yet unknown.
The attack happened near the former royal palace in the west of the city. The district is also home to several government buildings.
Violence across Afghanistan is at its highest level since the US-led invasion of the country ten years ago, according to the United Nations.
NATO has more than 130,000 troops stationed there. They are set to leave by the end of 2014.