Army Gen. Xavier Brunson testifies during a Armed Services hearing to examine his nomination to be general and Commander, United Nations Command Combined Forces Command United States Forces Korea on Capitol Hill Tuesday, Tuesday, in Washington. (AP)

The US Forces Korea commander nominee on Tuesday described North Korea's "rapid" advancement of its nuclear and missile capabilities as the "single greatest" challenge facing the Korea-based command, vowing to maintain a "constant" state of readiness if confirmed.

During a confirmation hearing of the Senate Armed Services Committee, Lieut. Gen. Xavier Brunson, currently the commander of First Corps, also voiced concerns over growing military exchanges between Pyongyang and Moscow, noting his commitment to mitigating risks associated with their military alignment.

The hearing took place as North Korea has ratcheted up tensions on the Korean Peninsula through missile launches, a rare disclosure of a uranium enrichment facility, the sending of trash-filled balloons to the South and other worrisome activities.

"I am aware of the threat South Korea faces, and fully understand (that) my role, if confirmed, is in ensuring a constant state of readiness for all forces on the peninsula. Most assuredly, I understand the need to defend the homelands," Brunson said in his opening remarks, portraying South Korea as one of America's "preeminent" and "finest" allies.

"North Korea's rapid advancement of its nuclear and missile capabilities, combined with its stated ambition to exponentially expand its nuclear arsenal, is the single greatest challenge facing the tri-command. The phrase, 'fight tonight,' is not just a saying, but a reality for the men and women serving in Korea," he added.

The tri-command refers to the three commands that he would lead if confirmed -- South Korea-US Combined Forces Command, United Nations Command and the 28,500-strong USFK. Currently, the commands are led by Gen. Paul LaCamera.

Asked about how he will reassure South Korea of America's nuclear umbrella, Brunson noted the importance of information sharing as well as conventional and nuclear assurances to the Asian ally.

"Sometimes, the best way to do that is to recognize where the adversary is maneuvering at ... I would, in my own military estimation, say that he was maneuvering in the information space," he said.

"Where I would start at is to come close to our partner, our ally in Korea, and explain to them what we are seeing and then trust again our diplomats and others to continue to have higher-level discussions. But at its base, it's being able to assure our partner and ally that we are there, and they can exist under not only a conventional umbrella but a nuclear umbrella on the peninsula."

Commenting on the North's recent disclosure of a uranium enrichment facility, the nominee assessed that the recalcitrant regime is trying to "maneuver in the information space" by revealing something hidden for long.

"If I am confirmed, I have to take a look at how are we maneuvering in the information space to counter the narratives that are put forward by that ... That causes tectonic shifts amongst Korean people when they see another facility because we all know that a facility that you can process uranium in is a facility that you can make warheads," he said.

To outmaneuver the North in the information space, Brunson stressed the importance of working together with Indo-Pacific Command and others in a multilateral approach.

"Any maneuver is met with other maneuver, and so we've got to meet them in that space and alleviate some of those changes," he said.

Casting the deepening ties among North Korea, China and Russia as a "quid pro quo" relationship, Brunson underlined the need to keep close tabs on what North Korea is getting in return for its arms transfers to Russia.

"The exchange of lethal aid between the DPRK and Russia is a thing to be alarmed about. But most importantly, what we have to do is see what's coming back in," he said, referring to the North by its official name, the Democratic People's Republic of Korea.

"In order to see that, it's going to take the IC (intelligence community) to help us see and understand what's coming back because if confirmed, my job as a USFK commander would be to mitigate that."

In the relationship among Pyongyang, Beijing and Moscow, there are also "opportunities" that the US and its allies should be cognizant of, the nominee pointed out.

"Because there might be a fissure between China and DPRK now that they are looking toward Russia," he said. "I think that the quid pro quo relationship amongst the authoritarian colluders ... I think that's going to be there. And I think that's the assailable flank that we have to deal with things early and often."

Brunson positively viewed progress in trilateral security cooperation between Seoul, Washington and Tokyo, saying that it is "trending upwards strongly." He particularly noted improvement in military exercises and information sharing among the countries.

"What those things provide for us is an opportunity that hasn't existed before," he said.

He went on to say that if confirmed, he would try to find ways to bring not only Northeast Asian allies together, but also to bring other allies and partners for regional security.

Touching on the South Korea-US Nuclear Consultative Group, the allies' nuclear deterrence body, Brunson called it an avenue available to provide the US' security assurance to Seoul.

"What I do believe is that the NCG has gone to great lengths to bring us closer to be able to talk about a lot of these issues," he said.

He also mentioned South Korea's contributions to the maintenance of facilities at Camp Humphreys, a key US military base in Pyeongtaek, about 65 kilometers south of Seoul, when he was asked about the ongoing negotiations between Seoul and Washington over a defense cost-sharing deal.

"I am not negotiating that agreement at all. The State Department is well involved in that," he said.

"But what I will tell you is ... I've seen Camp Humphreys ... in the housing that's available to our families there, the resources that are available to those families there ... much of that done by the Korean government."

Brunson has been commanding I Corps, which is the Army's operational headquarters for the Indo-Pacific. The unit manages the daily activities of more than 40,000 service members across the Indo-Pacific, including personnel stationed in Washington, Hawaii and Alaska, according to the Army.

He has served in various key defense positions in both conventional and special operations forces, according to the Army. His operational assignments included deployments to Iraq and Afghanistan. (Yonhap)