The highly symbolic rail service started last month as a way to ship goods to and from a joint North-South industrial complex in Kaesong, just north of the border. It is the first train service between the countries in more than half a century.
But the train has run empty many times because South Korean companies running factories in the industrial zone are reluctant to use the service because transporting goods by bus is more convenient and costs less, according to a South Korean Defense Ministry official.
The Defense Ministry official said a North Korean colonel holding working-level military talks with the South told his counterparts that it would be better to reduce the number of trains rather than have them running without freight.
The two countries are scheduled to hold rail talks on January 29 to 30 in Kaesong.
The opening of the train service was one of the tangible results of an October summit between North Korean leader Kim Jong Il and South Korean President Roh Moo-hyun that outlined a series of joint projects.
The two sides also agreed in principle last month to allow passengers to use the train service to go to Kaesong starting this year. But details have yet to be worked out, and it is unclear when the service can start.