Seoul, South Korea ? The blast was so big that some North Koreans thought a nuclear war had erupted.

In the aftermath, it looked like a giant fireball had ripped across the landscape, leaving a trail of scorched earth and devastation for a radius of 500 yards around the Ryongchon train station.

This was the scene 48 hours after the terrible conflagration in the North Korean town, as observed by a delegation of diplomats and aid workers who were brought up to the site Saturday. The accident claimed 154 lives and injured 1,300 people, according to figures the North Korean government supplied to U.N. agencies working in Pyongyang, the capital.

In its first statement on the accident, North Korea said it was caused by “electrical contact caused by carelessness during the shunting of wagons loaded with ammonium nitrate fertilizer.” The North Koreans further told the diplomats that a railcar filled with fuel was involved. Other accounts have suggested that two trains collided.

The U.N. agencies said that the force of the explosion destroyed or damaged about 40 percent of Ryongchon, an industrial town of 27,000.

North Koreans said that the blast was so deafening they had initially thought the United States had dropped a nuclear bomb — an event widely predicted by North Korea’s fiercely anti-American propaganda machine.

“My first thought was, ‘Now they’ve dropped it,'” Kaija Rajahuhta, an aid worker with the International Red Cross, was told by one North Korean.