By Phil Stewart and David Brunnstrom

WASHINGTON (Reuters) – The top U.S. commander in the Pacific told Congress on Wednesday the United States may need to strengthen its missile defenses, particularly in Hawaii, given the advancing threat from North Korea’s missile and nuclear weapons programs.

Just before the entire U.S. Senate was due to receive a top-level briefing on North Korea at the White House, Admiral Harry Harris said he believed Pyongyang’s threats against the United States needed to be taken seriously.

Graphic – Carl Vinson strike group: http://tmsnrt.rs/2pqOMWA

Graphic – North Korea’s nuclear program: http://tmsnrt.rs/2n0gd92

Earlier on Wednesday, the U.S. military moved parts of an anti-missile defense system to a deployment site in South Korea, triggering protests from villagers and by China – whose help is vital to agreeing and implementing tougher economic sanctions to try to persuade North Korea to abandon its weapons programs.

North Korea’s growing nuclear and missile threat is perhaps the most serious security challenge confronting U.S. President Donald Trump. He has vowed to prevent North Korea from being able to hit the United States with a nuclear missile.

Harris told lawmakers the Terminal High Altitude Area Defense (THAAD) system would be operational “in coming days.”

He said the defenses of Hawaii were sufficient for now but could one day be overwhelmed, and suggested studying stationing new radar there as well as interceptors to knock out any incoming North Korean missiles.

“I don’t share your confidence that North Korea is not going to attack either South Korea, or Japan, or the United States … once they have the capability,” Harris told one lawmaker.

Washington and Pyongyang have stepped up warnings to each other in recent weeks amid concerns that Pyongyang may soon conduct a sixth nuclear bomb test.

Washington has said all options are on the table, including military strikes, but officials have stressed that the current focus is on stepped-up sanctions on North Korea, which are expected to be discussed at a U.N. Security Council meeting on Friday chaired by U.S. Secretary of State Rex Tillerson.

Harris’s testimony was the latest sobering reminder of growing U.S. alarm about North Korea. The country has yet to test a missile capable of reaching the United States, but experts say it could have the capability some time after 2020.

U.S. officials have warned that a conflict with North Korea could have a devastating effect on ally South Korea and U.S. troops based there, a point Pyongyang underscored by a big live-fire exercise on Tuesday to mark the foundation of its military.Harris conceded that North Korean retaliation to any U.S. strikes could cause many casualties in South Korea, but added that there was the risk “of a lot more Koreans and Japanese and Americans dying if North Korea achieves its nuclear aims and does what (North Korean leader Kim Jong Un) has said it’s going to do.”

North Korea has vowed to strike the United States and its Asian allies at the first sign of any attack on its territory.

SHOW OF FORCE

In a show of force, the United States is sending the USS Carl Vinson aircraft carrier group to waters off the Korean peninsula, where it will join the USS Michigan, a nuclear submarine that docked in South Korea on Tuesday. South Korea’s navy has said it will hold drills with the U.S. strike group.

Harris said the carrier was in the Philippine Sea, within two hours’ striking distance of North Korea if need be.

The earlier-than-expected steps to deploy the missile defense system were denounced both by China, where the foreign ministry vowed Beijing would “resolutely take necessary steps to defend its interests,” and the frontrunner in South Korea’s May 9 presidential election.

Moon Jae-in has called for a delay in the deployment, saying the new administration should make a decision after gathering public opinion and more talks with Washington.

A spokesman for Moon said moving the parts to the site “ignored public opinion and due process” and demanded the deployment be suspended.

Television footage showed military trailers carrying equipment, including what appeared to be launch canisters, to the battery site.

More than 10 protesters were injured in clashes with police, Kim Jong-kyung, a leader of villagers opposing the deployment, told Reuters. Kim said about 200 protesters who rallied overnight would keep up their opposition.

Beijing says the system’s advanced radar can penetrate deep into its territory and undermine its security, but Harris scoffed and suggested Beijing should focus on trying to influence North Korea.

In another move likely to irk China, Harris said he thought there would soon be more U.S. freedom of navigation operation in the South China Sea.

China claims almost the entire South China Sea, where about $5 trillion worth of sea-borne goods pass every year, and has angrily protested previous U.S. operations there.

Harris sought to separate the issue from North Korea.

“We should encourage China and be appreciative of what they are doing with regards to North Korea and we should also be willing to criticize them for their aggressiveness and coerciveness in the South China Sea,” he said.

North Korea’s foreign ministry called U.S. attempts to make Pyongyang give up its nuclear weapons through military threats and sanctions “a wild dream” and like “sweeping the sea with a broom”.

Chinese Foreign Minister Wang Yi urged all sides to ease tensions and work toward a peaceful solution through negotiations.

“Security and stability is quite fragile and there is a great danger that a new conflict, or incidents could happen at any time,” he said.

U.S. officials say Washington sees no value in returning to international talks on North Korea until Pyongyang shows it is serious about denuclearization.

(Additional reporting by Ben Blanchard in Beijing and Phil Stewart, David Brunnstrom and Patricia Zengerle in Washington; Editing by Clive McKeef and James Dalgleish)