(Updates with airport reopened)

KHARTOUM, April 7 (Reuters) - A large Sudanese army truck full of ammunition exploded in Khartoum on Saturday, but caused no casualties, an army spokesman said.

"The truck was shaken and this caused the explosion," the spokesman said.

He did not say what might have caused the blast. Al Jazeera television quoted an unnamed security source as saying the ammunition exploded because of the hot weather.

"There are still blasts caused by the initial explosion and fire engines are not able to reach the area. But there are no casualties so far," the spokesman told Reuters.

The state-run Sudanese Media Centre (SMC) quoted the official armed forces spokesman, Mohamed Aghbash, as saying in a statement that the accident took place inside an ammunition site.

An ambulance was seen heading towards the site of the explosion. Security forces cordoned off the area. Explosions could be heard for about two hours after the indicent

A former Reuters correspondent said the explosion caused the international airport to be closed down.

Irwin Arieff said the steward on his KLM flight announced the safety of the aircraft could not be guaranteed because of shrapnel in the area.

The airport later reopened.

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