North Korea experts say the country has made progress in missile launch systems. They say its launch systems could send a nuclear bomb as far as the United States.
The U.S. military says it is concerned about North Korea's development of small nuclear devices and missile launchers.
The commander of U.S. Forces Korea spoke to reporters late last week about North Korea's missile launch systems. Army General Curtis Scaparrotti said North Korea has the right technology to develop a small nuclear weapon that can work with a mobile launcher.
A few days later, the South Korean Defense Minister said the North's ability to reduce the size of a nuclear weapon appears to have reached what he called "a significant level." He also said he believes North Korea is able to build a uranium-based nuclear bomb.
Bruce Bechtol is with Angelo State University in Texas. He also served as president of the International Council on Korean Studies. He told VOA that North Korea observers have thought for years that the country possesses that technology.
"North Korea has a highly enriched uranium program. They probably had it weaponized by 2010. Which means they probably had a device small enough to put on a missile — probably the Nodong — four years ago."
The Nodong or Rodong 1 is a North Korean ballistic missile. After the missile is launched from North Korea, it could fly as far as Japan.
Mr. Bechtol said he is even more concerned about the plans for North Korea's KN-08 missile, which can travel even greater distances. He said such a missile could hit the United States.
Also worrying is North Korea's development of mobile missile launchers. Mr. Bechtol says those launchers are difficult to detect by satellite.
"The United States is very worried about this. It's also very worried about the new long range mobile missile that the North Koreans have, that is the KN-08, and I think that is something that has come as rather a surprise in the past couple of years."
North Korea has violated United Nations Security Council resolutions with nuclear tests, short-range missile launches, and the launch of a small satellite into space.
Groups that support stronger measures against North Korea say the U.S. military should take preventive action. One of their ideas is to bomb North Korean missile sites.
But North Korea expert Sergey Radchenko disagrees. Mr. Radchenko is with Britain's Aberystwyth University. He says a strike against North Korea would risk pushing the region into war.
"The hawks, who call for tougher measures, will be counteracted by people who will say we can't really do it. We cannot afford to do anything because of deep uncertainty with regard to the North Korean nuclear program and even with the fact that they have conventional capabilities."
Even opponents of military action against North Korea say the development of smaller weaponry and launchers is a growing threat. But they expect the United States will continue to deal with North Korean threats with restrictions, the promise of aid and a strong military presence in South Korea.
I'm Anne Ball.