The explosion rocked the city on Thursday, but there was no immediate report of casualties.

“We can confirm an explosion outside of ISAF HQ around 1020 (am), no other information at this time,” ISAF said in a statement.

The explosion triggered the US embassy to sound “duck and cover” sirens.

Lutfullah Mashal, a National Directorate of Security (NDS) official, said that the blast was “an accident, not an enemy act.”

“The blast happened in a depot for unexploded ordinance. It was totally an accident. There is no reported casualties but there are some damages.”

The blast came a day after a member of the Taliban exploded an explosives-laden vehicle near a NATO military convoy entering the international airport in Kabul.

The airport is home to one of the most important bases belonging to US-led NATO forces in Afghanistan. The base is responsible for the day-to-day management of the US-led war in Afghanistan.

Afghan sources also confirmed that the attack was against German soldiers, but said there had been no reports of casualties.

The US and its allies invaded Afghanistan in 2001 as part of Washington’s so-called war on terror. The offensive removed the Taliban from power, but the country is still gripped by insecurity.