WASHINGTON – The commander of U.S. forces in South Korea said on Friday he believes Pyongyang has the capability to build a nuclear warhead that can be mounted on a ballistic missile, but added there were no tests or other evidence it has taken that step.

Army General Curtis Scaparrotti said he thought North Korea’s connection with Iran and Pakistan meant it probably had access to the expertise needed to miniaturise and mount an atomic weapon on a missile.

“I believe they have the capability to miniaturise a device at this point and they have the technology to potentially deliver what they say they have,” Scaparrotti told a news conference at the Pentagon.

“We’ve not seen it tested, and I don’t think as a commander we can afford the luxury of believing perhaps they haven’t gotten there,” he added.

Rear Admiral John Kirby, the Pentagon press secretary, said later that Defense Secretary Chuck Hagel shared Scaparrotti’s concerns about North Korea’s progress toward a nuclear weapon, but added the general had not said Pyongyang was able to mount a weapon on an intercontinental ballistic missile.

“General Scaparrotti said he believes they have the capability to miniaturise,” Kirby said. “That’s not the same thing as saying that they have the capability to mount, test and deliver a nuclear weapon in an ICBM.”

No one outside of the inner circle of North Korea’s nuclear programme likely knows what advances the country has made. But mastering the step of miniaturising a nuclear warhead would put Pyongyang far closer to its long-stated goal of acquiring a nuclear deterrent and make a mockery of years of U.N. sanctions aimed at curbing such a programme.

North Korea has conducted three tests of nuclear devices, the most recent in February 2013. But miniaturising the device, so it can be fitted into a delivery system like a bomb or missile, is a technological hurdle that has to be crossed in creating a nuclear weapon.Asked if Pyongyang actually had miniaturised a nuclear device, Scaparrotti said: “I don’t know that.”

“What I’m saying is … that I think given their technological capabilities, the time that they’ve been working on this, that they probably have the capabilities to put this together,” he said.

Scaparrotti indicated the road-mobile missile launcher and KN-08 intercontinental ballistic missile North Korea has paraded publicly were a concern. Despite Pyongyang’s aggressive missile development programme, analysts have been divided on whether the military hardware was functional missile or a mock-up.

Scaparrotti also said there was no indication of political struggle or turmoil in North Korea recently when leader Kim Jong-un disappeared from public view for several weeks. He reappeared in the middle of the October with a limp and a cane, leading to conclusions he had a health issue.

“We didn’t see any discernible change that led us to believe there was any instability … during the time that he was gone,” the general said, adding it “looked like very normal functioning of their government in the country at that time.”

He said Kim remained in control of an “isolated, authoritative regime that’s willing to use violence and threats of violence to advance its interests.”

The 1950-53 Korean war ended in an armistice agreement and the peninsula remains divided between the North and South, which is closely allied with the United States.

(Reporting by David Alexander; Editing by Tom Brown)