North Korea has said its ruling Workers Party will hold its first congress in nearly 40 years next month.
The gathering, which will take place in Pyongyang from 6 May, will be only the seventh in the party's history and the first under leader Kim Jong-un.
It will be closely watched for signs of major policy shifts, movement among senior officials or comment on North Korea's nuclear programme.
It comes as North Korea is believed to be preparing a fifth nuclear test.
North Korea has often timed its controversial tests to coincide with big political occasions.
Its fourth test, in January, was followed by the launch of a satellite.
Both were violations of existing sanctions and resulted in the UN imposing further measures limiting trade and contact with the North, foreign media reports.