Korea's geostationary weather-communications satellite the Cheollian had to be deflected earlier this week to prevent it from colliding with a Russian military communications satellite.

The Korea Aerospace Research Institute says the Raduga 1-7 came within three km of the Cheollian's orbit at 128.2 degrees east longitude between Monday and Tuesday.

The institute quickly revised Cheollian's orbit using a satellite thruster and is keeping a close watch on it. The Cheollian is currently 120 km from the Russian satellite.

The Raduga 1-7's abrupt movement also caused two Japanese satellites to be deflected.

Seoul and Tokyo have jointly asked for an explanation from Russia, but Moscow has not responded yet.