A large explosion outside NATO's International Security Assistance Force (ISAF) headquarters rocked central Kabul on Thursday, although there was no immediate confirmation of casualties.

The blast triggering the US embassy's "duck and cover" sirens.

"We can confirm an explosion outside of ISAF HQ around 1020 (am), no other information at this time," ISAF said on its official Twitter account.

The blast came the day after a Taliban suicide bomber detonated an explosives-laden vehicle near a NATO military convoy entering the city's airport, killing himself but causing no other deaths or injuries.