SEOUL, South Korea >> North Korea on Wednesday caused a new stir by publicizing a purported mock-up of a nuclear warhead for the first time, with leader Kim Jong Un saying his country has developed miniaturized atomic bombs to be placed on missiles.

The North’s Rodong Sinmun newspaper carried photos on its front page that showed Kim and nuclear scientists standing beside what outside analysts say appears to be the model warhead — a small, silverish globe presented on a low table in a hangar with a ballistic missile or a model ballistic missile in the background.

The newspaper said Kim met his nuclear scientists for a briefing on the status of their work and declared he was greatly pleased that warheads had been standardized and miniaturized for use on ballistic missiles.

South Korea’s Defense Ministry said Wednesday it was analyzing the objects shown in the photos.

It was the first time the North has publicly portrayed what its designs look like, though it remains unclear whether the North has a functioning warhead of that size or if it is simply trying to develop one.

The disclosure comes amid heightened tensions in the wake of harsh U.N. sanctions on North Korea for its nuclear test and long-range rocket launch earlier this year. North Korea warned Monday of pre-emptive nuclear strikes after the United States and South Korea began holding their biggest-ever war games, which will go on until the end of April.

Pyongyang has previously said it has nuclear warheads small enough to put on long-range missiles capable of striking the U.S. mainland, but experts have questioned such claims.

The round object shown in the photos appears to be a model of a trigger device for a warhead, which would contain uranium or plutonium inside it, according to nuclear expert Whang Joo-ho of Kyung Hee University in South Korea. He said it was obviously a model because Kim and the others in the photos would not stand near it because of concerns of radioactive leaks if it was a real warhead. In the photos, no one was seen wearing radiation suits or protection.

Whang said it was impossible to judge from the photos if North Korea has mastered the miniaturization technology because it was not known if the object was real or not. But he said its shape looks similar to ones used in existing nuclear warheads developed by other countries.

The North says it tested its first H-bomb on Jan. 6, followed last month by the launch of a rocket that put a satellite into orbit but which was violating U.N. resolutions because it contains dual-use technology that could also be applied to long-range ballistic missiles.

Its development of smaller nuclear weapons and long-range missiles that could be used to deliver them to targets overseas has long been a matter of concern and could potentially shake up the security balance in Asia.