North Korea's New 'Number Two'?

North Korea signaled a key leadership change with the announcement Friday that the man seen as supreme leader Kim Jong-Un's number two had been replaced as political chief of the military.

In a report on May Day celebrations in Pyongyang, the North's official KCNA news agency named Hwang Pyong-So as the director of the Korean People's Army (KPA) General Political Bureau, not Choe Ryong-Hae, who previously held the position.

The post is generally viewed as the second most important in the military after Kim, who is supreme commander.

The leadership change comes amid growing concerns that the North is preparing to conduct a fourth nuclear test in the face of stern international opposition after satellite images showed a recent increase in activity at the country's main test site.

"To all intents and purposes, this makes Hwang, who also has close personal ties to Kim Jong-Un, the second most powerful man in the country," said Michael Madden, author and editor of the NK Leadership Watch website.

Hwang's appointment came just days after KCNA reported his promotion to the rank of vice marshall on April 28 -- a rank shared with Choe and just four others.

It was not immediately clear what had become of Choe, who was widely believed to have moved into the role of North Korea's unofficial number two following the execution in December of Kim's uncle and political mentor, Jang Song-Thaek.

Choe holds a number of other top positions as a politburo standing committee member and a vice chairman of both the Central Military Commission and the National Defence Commission.

There were multiple reports earlier this year that Choe had been arrested and possibly purged after he dropped from public view for three weeks -- an unusually long absence for such a senior figure.

His reappearance in March, alongside Kim, led to speculation that his disappearance might have been due to health problems.

"I don't think we can say Choe has been purged, but he's clearly been moved aside, possibly for health or other reasons," said Yang Moo-Jin, a professor at the University of North Korean Studies in Seoul.

Yang agreed that Hwang was now effectively number two in the country, given his military rank, position and personal access to the supreme leader. 

Hwang, 64, was a top official in the ruling party's Organization Guidance Department (OGD) with a portfolio that included the physical and political protection of Kim Jong-Un.

According to Madden, his name started to emerge in the mid-2000s around the time Kim Jong-Un's father Kim Jong-Il was finalising arrangements for who would succeed him as leader.

"He became one of Kim Jong-Un's mentors and has been close to him for around 10 years, so he's been groomed for this role," Madden told AFP.

Hwang was said in the KCNA report Friday to have addressed a banquet in Pyongyang held for workers at a textile mill, attended by KPA commanding officers.

A report on KCNA earlier in the week said Hwang accompanied Kim on a tour of a newly built workers' hostel at the mill but made no mention of Choe, sparking initial speculation of the leadership shuffle.

Rumors about changes at the top of the Pyongyang regime intensified following Jang Song-Thaek's execution.

In February, North Korea promoted a host of key military officials including the chief of its rocket unit, the Strategic Rocket Force Command, which is in charge of the country's mid and long-range missiles program.

Ranking the leadership is North Korea is often a matter of educated guesswork, and some analysts warned that the "number two" label could be misleading, given the complex, opaque workings of the official and personal networks that determine genuine power in Pyongyang.

"In one way, there is no real 'number two'," said Dan Pinkston, North East Asia Deputy Project Director with the International Crisis Group in Seoul.

"There's the number one, and then there's everybody else, some of whom get closer to the seat of power than others for certain periods of time," Pinkston said.