North Korea seems to have the ability to miniaturize a nuclear warhead for its medium-range missiles, but does not appear technically ready to conduct necessary tests, a U.S. expert said Thursday.

"My analysis is that North Korea could probably miniaturize a warhead that should fit for a Rodong missile," Mark Fitzpatrick, director of the Non-Proliferation and Disarmament Program at the U.S.-based International Institute for Strategic Studies (IISS), said in an interview with Yonhap News Agency. "Probably not as Scud missile, which has a smaller diameter, but Rodong most probably." 

Last week, Gen. Curtis Scaparrotti, the top commander of U.S. forces in South Korea, told reporters that he believes Pyongyang has the capabilities to build nuclear-tipped missiles, although he has no evidence to confirm his assumption.

Fitzpatrick is in South Korea to take part in the 3rd Seoul Defense Dialogue underway for a three-day run since Wednesday. The multilateral vice ministerial-level forum has gathered hundreds of officials and security experts from 24 counties and three international organization.

Noting that it is "logical that they would be making progress in being able to produce the miniaturized warhead," the expert said Pyongyang would need to test it "at least once more to perfect the process."

"Probably, the North knows how to do it based upon their technical abilities, but until they test the miniature warhead, they would not be sure. In the process of the warhead development, it takes several tests to get it right," he said.

North Korea has carried out three nuclear tests since 2006, including its most powerful one in February last year, and the bellicose state has threatened to carry out "a new form" of underground test. 

"I've been anticipating (the fourth test) for a year ... Maybe North Korea is not just ready yet technically," Fitzpatrick said.

"The test site has been almost ready for a year, but they did not complete preparations. This means they've been waiting to complete preparations ... for some technical reasons we don't know."

As the unruly nation has not showed signs of any willingness to "barter its nuclear assets in exchange for a peace treaty and economic assistance," he called on South Korea, the U.S. and China, as well as the rest of the world, to work closely to deter Pyongyang.

"China has been cooperating with the U.S. in putting some pressure on North Korea, but China can do more as it has an economic leverage" albeit limited, he said.  

Speaking of the recent decision to delay the transfer of wartime operational control (OPCON) of South Korean troops from Washington to Seoul, he said it was "not absolutely necessary" but "a reasonable response to North Korea's provocations."

"It sends an important signal to North Korea that when they are belligerent and posing a threat, it has negative consequences for them," he said. 

South Korea was scheduled to regain wartime command in December 2015 after handing it over to the U.S. during the 1950-53 Korean War, but asked for a delay last year in the wake of the North's third nuclear test. Last week, the allies agreed to push back the date until the mid-2020s when South Korea is expected to acquire key assets to counter the North's nuclear and missile threats. 

"The only real solution to the problems of North Korea is the disappearance of North Korea ... Eventually it will succumb to greater economic and political strength of South Korea," he said. (Yonhap)