The nation's would-be first astronaut Ko San has been replaced just a month before he was to travel to space. Backup trainee Yi Soyeon will go instead.

Announcing the decision Monday, the Education, Science and Technology Ministry said Russia requested the change as Ko had broken training regulations.

Russian officials said they warned Ko several times against borrowing books unrelated to training. After he failed to comply, they are said to have asked Seoul to step in.

The ministry decided to switch candidates in a meeting Monday morning.

Ko and Yi were chosen as the final two in December 2006 from a pool of 18-thousand candidates. The top-ranked Ko had been training with two Russian astronauts to go into space aboard the Russian Soyuz spacecraft on April eighth. Yi had been training as a backup.

Yi will conduct scientific experiments at the International Space Station during her ten-day mission.