South Korea's military warned North Korea on Monday to immediately stop preparations for a spy satellite launch, vowing to take "necessary measures" if it goes ahead.

North Korea is preparing to launch a spy satellite for the third time, after failing twice this year to put a military eye in the sky.

Earlier this month, Seoul's spy agency said that Pyongyang was in the final stages of preparations for its third try and South Korean defense minister Shin Won-sik said Sunday that the lift-off could take place as early as this week.

"We sternly warn North Korea to... immediately suspend the current preparations to launch a military spy satellite," said Kang Ho-pil, chief director of operations at the Joint Chiefs of Staff.

"If North Korea goes ahead with the launch of a military reconnaissance satellite despite our warning, our military will take necessary measures to guarantee the lives and safety of the people," he added.

After a failed second attempt in August, Pyongyang said it would carry out the third launch in October, though it never materialised.

South Korea has said Pyongyang is providing Moscow with arms in exchange for Russian space technology.

Analysts have said there is significant technological overlap between space launch capabilities and the development of ballistic missiles, from which Pyongyang has been banned under multiple UN sanctions.

North Korea has conducted a record number of weapons tests this year, ignoring warnings from the United States, South Korea and their allies.

Last week, it said it carried out successful ground tests of a "new type" of solid-fuel engine for its banned intermediate-range ballistic missiles, calling it a crucial step against "the grave and unstable security environment".