South Korea will buy two French spy planes capable of intercepting radio messages from North Korea and detecting its missile launches, a state agency said Monday.

The Falcon 2000 reconnaissance planes will be purchased from defence firm Dassault, probably in 2017, the Defence Acquisition Programme Administration said in a statement.

The French planes will replace some of South Korea's ageing spy planes including RC-800s built by US firm Raytheon, it said.

Compared to the RC-800, the Falcon 2000 has a longer range and can carry more equipment, the agency said.

The South has generally favoured defence equipment from the United States, which has based troops in the country since the 1950-1953 Korean War to deter aggression by the North.

In an effort to reduce its heavy dependence on US-operated reconnaissance aircraft, South Korea will also buy four high-altitude surveillance planes from Boeing by the end of 2012.

The first of the modified Boeing 737 Airborne Early Warning and Control (AEW&C) planes was delivered to the South's air force this year.

It can track airborne and maritime targets simultaneously and direct fighter jets and ships to engage them.