Japan said Monday it had been informed by Pyongyang that a satellite launch could happen as early as this week, but Tokyo warned the North may in fact be planning a sanctions-defying ballistic missile test.

KCNA cited Ri Pyong Chol, vice-chairman of the ruling party's central military commission, as saying the "military reconnaissance satellite No. 1" would be "launched in June".

That satellite, along with "various reconnaissance means due to be newly tested, are indispensable to tracking, monitoring... and coping with in advance in real time the dangerous military acts of the US and its vassal forces", the statement said.

Citing "reckless" acts by Washington and Seoul, Ri said North Korea felt "the need to expand reconnaissance and information means and improve various defensive and offensive weapons" in an effort to bolster military preparedness.

The official also accused the United States of conducting "hostile air espionage activities on the Korean peninsula and in its vicinity".

North Korea informed Japan it will launch a rocket between May 31 and June 11, identifying waters near the Yellow Sea, the East China Sea and to the east of Luzon Island in the Philippines as warning areas, a Japanese coast guard spokesman told AFP.

Such zones are usually designated for falling debris or rocket stages.

In 2012 and 2016, Pyongyang tested ballistic missiles that it called satellite launches. Both flew over Japan's southern Okinawa region.

North Korean leader Kim Jong Un this month inspected the country's first military spy satellite as it was prepared for launch, and gave the green light for its "future action plan".