North Korean leader Kim Jong Un has encouraged researchers on the country's atomic bomb programme to work for "greater successes" on the nuclear weapons project.
Kim praised the scientists, technicians and workers for contributing to what North Korea claimed was its first successful test of a hydrogen bomb, state media reported on Monday.
The staff greeted Kim enthusiastically and the leader posed with them for a photo, official news agency KCNA said.
The test Wednesday caused outrage worldwide, although the regime's claim that it tested a hydrogen bomb has met with scepticism abroad.
Experts said initial analyses of the tremors indicated the testing of a normal atomic bomb rather than the much more powerful hydrogen bomb.