Attention is focused on whether North Korean leader Kim Jong Un will refer to the planned launch of what the country calls an "artificial satellite" at a key meeting of the ruling Workers' Party early next month.

North Korea has notified the Japanese government that it will launch a satellite between May 31 and June 11. Japanese officials suspect Pyongyang plans to launch a ballistic missile under the pretext of putting a satellite into orbit.

The Workers' Party newspaper Rodong Sinmun reported on Monday that the Political Bureau of the party's Central Committee had decided the previous day to convene the plenary meeting of the committee in early June.

The newspaper said the meeting, the first of its kind since March, will discuss policy issues of "weighty significance in the development of the country's revolution."

On May 16, Kim inspected the country's No.1 military reconnaissance satellite and approved the next steps of an action plan for the spy satellite. But he did not disclose the timing of the launch.

Last week, a US-based research group, 38 North, released its analysis of satellite images of North Korea's Sohae Satellite Launching Station in Tongchang-ri in the country's northwest.

The group said construction at the site is "moving forward at a remarkable pace."