SEOUL (Reuters) - North Korea will issue "an important report" at noon local time(0300 GMT), its state news media said on Wednesday.
"An important report will be issued in the DPRK at 12:00 (local time) Wednesday," KCNA news agency said in a single-line dispatch.
No further details were given by the reclusive state, although the last time the agency used this wording was when leader Kim Jong-il died in December.
The statement caused financial markets in Seoul to fall sharply.
The announcement comes after new leader Kim Jong-un, a son of Kim Jong-il, reshuffled his top military over the past few days, ousting a senior general.
Vice Marshal Ri Yong-ho, who was seen as close to Kim Jong-il, was relieved of his posts in the Workers' Party of Korea at a politburo meeting on Sunday, including the powerful role of vice chairman of the Central Military Commission, KCNA said.
A relative unknown, Hyon Yong-chol, was promoted to vice marshal, but it was not known whether Hyon would replace Ri as head of the North Korean army, one of the world's largest.
One of the main beneficiaries of Vice Marshal Ri's ousting looks to be Jang Song-thaek, the young Kim's uncle who married into the ruling family and who is reckoned by many analysts as the real power behind the throne.
A South Korean government report said Jang and Choe Ryong-hae, a long-time party faithful used as a counterbalance to Jang's influence, were behind Ri's ouster.
A spokeswoman for the South Korean presidency said she was not aware of what could be in the announcement. Authorities in Seoul also said there were no signs of a nuclear test by North Korea, which would be its third.
The North has been further isolated and squeezed by international sanctions, imposed for its nuclear and missile programs.
Kim Jong-un's brief term in office since his father's death is, at least on the surface, a sharp change from the former leader's dour rule which took North Korea deeper into isolation, abject poverty and large-scale political repression.
Once the official mourning period was over, the youngest Kim to rule North Korea was seen laughing with fusty old generals, gesticulating in delight at a military parade and, the biggest shock of all, speaking. Most North Koreans went to their graves never having seen Kim the elder speak.
(Reporting by Jack Kim; Editing by David Chance and Raju Gopalakrishnan)