A massive explosion has occurred at a North Korean railroad station near the Chinese border of Dandong, killing or injuring as many as 3,000 people.

The explosion reportedly happened about 1 p.m. Thursday in Ryongchon, a town 20 kilometers from the Chinese border.

The communist North has reportedly cut off international telephone lines in an apparent attempt to prevent details of the explosion from leaking out.

Seoul-based Yonhap News Agency said two fuel trains collided at the North Korean railroad station, igniting a deafening explosion that rained debris in an 8 kilometer radius.

Japan's Kyodo news agency quoted sources in Dandong as saying Pyongyang had requested assistance from China to cope with the disaster. Kyodo also quoted an unidentified U.S. official as saying the explosion was confirmed by satellite images, but that further details on the extent of damage and casualties were unavailable.

A South Korean government official said Seoul was working to find out the cause of the explosion and the exact number of casualties.

The official, however, dismissed speculation that the explosion may have been a failed attempt to assassinate North Korean leader Kim Jong-il, who passed safely through the station nine hours before the blast. The officials said the outdated and dilapidated condition of the North's railway facilities was more likely the cause of the disaster.

North Korean defectors residing in Seoul speculated that the explosion may have caused more than 3,000 casualties, citing a high population density in the area. The North Korean city of Ryongchon is known to have a population of 130,000.