North Korea has issued formal notice of a satellite launch as early as Wednesday, Japan said, defying warnings from South Korea and multiple UN resolutions banning Pyongyang from using ballistic missile technology.
The Japanese coast guard posted a notification on its website on Tuesday of a launch window between November 22 and December 1.
Japanese Prime Minister Fumio Kishida told reporters he had instructed government ministries and agencies "to make utmost efforts in collecting information and providing it to the Japanese people, to demand cancellation of the launch in cooperation with relevant countries, and to make utmost efforts in preparing for unpredictable situations."
He added that any use of ballistic missile technology would represent a breach of UN resolutions and that Japan was coordinating its response with South Korea and the United States, its partners in a trilateral defence arrangement.
Earlier this month, Seoul's spy agency said that Pyongyang was in the final stages of preparations for another effort to put a military eye in the sky.
South Korean Defence 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," Kang Ho-pil, chief director of operations at the South Korean Joint Chiefs of Staff, said Monday.
"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."
After a failed second attempt in August, Pyongyang said it would carry out the third launch in October, though it never materialised.
The UN Security Council has adopted many resolutions calling on North Korea to halt its nuclear and ballistic missile programmes since it first conducted a nuclear test in 2006.
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.
Russian President Vladimir Putin suggested in September after a meeting with North Korean leader Kim Jong Un that his nation could help Pyongyang build satellites.
Successfully putting a spy satellite into orbit would improve North Korea's intelligence-gathering capabilities, particularly over South Korea, and provide crucial data in any military conflict, experts say.
North Korea has conducted a record number of weapons tests this year, ignoring warnings from the United States, South Korea and their allies.