DANDONG, China -- Issuing a rare appeal for foreign help, North Korea's secretive government said Friday that a devastating train explosion killed several hundred people, and it invited aid workers to come see the disaster site near the Chinese border.

U.S. defense officials said damage from the blast extended at least 200 yards from the explosion at a railway station in Ryongchon, a city with chemical and metalworking plants and a reported population of 130,000.

American intelligence analysts regarded Thursday's blast as an industrial accident involving two trains but it was unclear what ignited it, the officials said, speaking on condition of anonymity.

The analysts thought it was probably a coincidence that the blast happened hours after North Korean leader Kim Jong Il reportedly passed through the station on his way home from a three-day visit to China.

There has been no unusual movement of North Korean military forces detected since the explosion, although it is likely some would aid in disaster recovery efforts, the officials said.

State Department spokesman Richard Boucher said the United States is evaluating the situation in North Korea to see "if there is a need or an opportunity for the United States to help."

He noted that the United States has provided humanitarian aid in the past to North Korea. He added that there are no obstacles to sending assistance in response to the current situation.

North Korean officials told diplomats and aid groups that more than 1,000 people were injured and thousands of apartments and houses destroyed or damaged in the blast.

They said many more could be trapped in collapsed buildings near the station. Red Cross workers were distributing tents and blankets to 4,000 families.

While the communist North appealed for help and disclosed some details of the blast to the outside world, its state-controlled domestic media remained silent on the disaster.

Aid workers said North Korean officials on Friday blamed an electrical accident with a train carrying explosives.

"What they've said is that two carriages of a train carrying dynamite -- they were trying to disconnect the carriages and link them up to another train," Anne O'Mahony, regional director for the Irish aid agency Concern, told Irish radio station RTE from Pyongyang, North Korea's capital.

"They got caught in the overhead electric wiring, the dynamite exploded, and that was the cause of the explosion," she said.

Accounts of the materials involved differed. John Sparrow, a Red Cross spokesman in Beijing, said the trains were carrying explosives similar to those used in mining. China's Xinhua News Agency reported the blast was blamed on ammonium nitrate -- a chemical used in explosives, rocket fuel and fertilizer -- leaking from one train. South Korea's unification minister said the trains were carrying fuel.

The blast leveled the train station, a school and apartments, South Korea's Yonhap news agency said, quoting Chinese witnesses. It said there were about 500 people in the station at the time.

South Korea's Chosun Ilbo newspaper, citing a South Korean intelligence source, said a U.S. spy satellite photograph showed damage mostly in densely populated neighborhoods east of the station, which included buildings for the military and ruling Workers' Party.

"Hospitals are jam-packed with people injured," Chosun Ilbo quoted a Chinese witness as saying.

There was no sign in Dandong, a Chinese border city about 12 miles from Ryongchon, of injured North Koreans. But the city's three biggest hospitals were preparing for a possible surge of patients.

"We're ready to offer our close neighbor our best medical help anytime," said an official at Dandong Chinese Hospital.

In Seoul, the South Korean capital, Unification Minister Jeong Se-hyun said China was urging North Korea to send the injured to hospitals in China. But he said Pyongyang was instead asking China to send in relief workers.

The explosion destroyed 1,850 apartments or houses and damaged 6,350, said Sparrow, citing officials in the North. The Red Cross reported at least 54 people killed and 1,249 injured, but Sparrow said "we are anticipating that the casualty figures will increase."