WASHINGTON -- North Korea has a "small number" of nuclear weapons, the vice chairman of the US Joint Chiefs of Staff said Thursday, although that number was not defined.

Air Force Gen. John Hyten told a virtual forum that the specific numbers were "classified" and in many ways hard to understand.

"But a small number is a confident characterization of nuclear capabilities that can threaten their neighbors or the United States," he said in a symposium hosted by the National Defense University's Center for the Study of Weapons of Mass Destruction.

Hyten offered no further explanation of what he meant by "a small number."

The US has never officially discussed its assessment of North Korea's nuclear capabilities, but the communist state is widely estimated to possess more than 70 nuclear warheads.

In its latest annual report," North Korean Tactics," published in July, the US Army said the North is "estimated" to possess 2,500 to 5,000 tons of chemical weapons.

With regard to its nuclear arsenal, however, the report simply states "estimates for North Korean nuclear weapons range from 20 to 60 bombs, with the capability to produce six new devices each year."

North Korea has conducted six nuclear tests, between October 2006 and September 2017.

Hyten's remark follows a recently renewed controversy, at least in Seoul, over Pyongyang's nuclear capabilities.

In his latest book, "Rage," Washington Post journalist Bob Woodward discusses a US response to a North Korean attack that he says could include the use of up to 80 nuclear weapons.

While the statement is largely believed to describe the US' possible use of nuclear weapons in response to an attack, some in South Korea insisted it described a North Korean attack that could include 80 nuclear weapons.

Hyten also stressed that US homeland defense starts not with its missile defense system but with its strategic deterrent.

"It's important that we realize that defense begins not with the missile defense capabilities, which I'm very confident can defend ourselves against the North Korean threat. But that's not where the defense of the homeland begins. The defense of the homeland begins with our strategic deterrent," he told the symposium.

The United States' deterrence includes the airmen that remain alert on their B-2 bombers and sailors on their Ohio-class submarines, Hyten said.

The US also continues to enhance its deterrent, he added, noting the B-2 bombers will soon be replaced by the B-21 and B-52 bombers and the Ohio-class submarines by the Columbia-class submarines armed with "nuclear weapons on board."

Later, speaking before the Senate Armed Services Committee, Adm. Charles Richard, the commander of the US Strategic Command, said the US also stands ready to deliver "a decisive response" should its strategic deterrence fail.

"North Korea, Iran continue to conduct harmful activities regionally, causing instability and threatening the United States, our allies and partners," said Richard.

"As a global combatant command, STRATCOM forces, my forces are prepared to respond to any contingency and should strategic deterrence fail. We stand ready to deliver a decisive response," the Navy admiral told the committee in the hearing broadcast online. (Yonhap)