KABUL, Afghanistan (AFP) - An accidental explosion in an arms depot shook central Kabul on Thursday, with Afghan officials moving quickly to allay fears of an attack on the city that has often been targeted by militants.

The loud blast erupted close to the Nato's International Security Assistance Force (ISAF) headquarters and in an area of the capital that houses many embassies and international institutions.

ISAF confirmed that the explosion occurred outside their headquarters, while the US embassy sounded its emergency "duck and cover" sirens to warn employees to seek shelter.

"It was an accident, not an enemy act," said Lutfullah Mashal, an official from the National Directorate of Security (NDS) intelligence agency.

"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 NDS said in a statement said that the depot contained explosives recently seized from insurgents and due to be taken to the Disbandment of Illegal Armed Group programme, which destroys illegal weapons and explosives.

An NDS spokesman told local television that the depot stored suicide vests, explosives and unexploded bombs.

The interior ministry also confirmed the explosion was an accident.

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

The airport houses another Nato base as well as operating civilian flights to cities including Dubai, New Delhi and Istanbul. Flights were delayed only briefly after the bomb exploded.

The Taliban, who regularly exaggerate casualty numbers, claimed responsibility via their main Twitter account for that attack, saying ten soldiers had been killed or injured.

Kabul has seen a recent drop in insurgent attacks after a series of high-profile strikes earlier this year, with the NDS claiming to have foiled several plots to launch complex strikes involving truck bombs and suicide gunmen.

A series of attacks earlier this year targeted foreign compounds, the Supreme Court, the airport and the presidential palace in the city.

Nato forces are withdrawing from Afghanistan after more than a decade of fighting the Taliban, but negotiations have stalled on a security accord that would allow some US and Nato troops to stay after 2014.

President Hamid Karzai was due to travel to India on Thursday, with US officials expressing hope that the Delhi government would be able to persuade him to sign the accord.