North Korea's nuclear capability is not believed to have increased despite the communist nation's latest nuclear test, a senior U.S. missile defense official said Tuesday.

"I would assess their technical capability has not increased,"

Vice Adm. James Syring, director of the U.S. Missile Defense Agency, said when he was asked about his assessment of the North's nuclear test during a discussion at the Center for Strategic and International Studies.

He didn't elaborate on the basis of his assessment.

"That said, everything they're doing continues to be alarming and provoking," Syring said. "And every step that we've taken with the program I briefed and our actions every day are vitally important to stay ahead of that threat. We continue to watch it closely and continue to watch its actions with scrutiny."

The official also said the North's test hasn't led to any change in the agency's missile defense program.

"There was no change before, there is no change now. We certainly watch all that testing and if it was warranted, you would see our program change. I believe we're absolutely on the right path to stay ahead of that threat," he said.

North Korea claimed the Jan. 6 test was a successful detonation of a hydrogen bomb.

But the White House expressed strong skepticism, saying "initial analysis is not consistent" with the North's claims. U.S.

nuclear experts have expressed doubts, saying its yield was too low to believe that such an advanced bomb, way more powerful than conventional nuclear weapons, had been detonated.

This was the North's fourth nuclear test, following detonations in 2006, 2009 and 2013.

The nuclear test has given rise to calls for expanded missile defenses, with South Korean President Park Geun-hye saying she would consider a possible deployment of the U.S. THAAD missile defense system according to national interests.

Syring said he has no update on the issue.

"As you know, formally, there's no discussions, no considerations. We continue to work with South Korea on a wide range of potential capabilities. I'll just leave it at that," he said. "That's in a totally different lane than mine. I'm the equipment provider. I'll let the policy and State Department officials work that side."

It is no secret that the U.S. also wants to deploy a THAAD unit to South Korea, where some 28,500 American troops are stationed, to better defend against ever-growing threats from North Korea's ballistic missile and nuclear programs.

But the issue has become one of the most sensitive for South Korea because China sees a potential THAAD deployment as a threat to their security interests and have increased pressure on Seoul to reject such a deployment.

Seoul and Washington have maintained they have never held any formal consultations on the issue. (Yonhap)