SEOUL--America’s top diplomat on Thursday pressed China to use its “tremendous influence” to convince North Korea to abandon its nuclear program, hours after the North said it will ignore U.S. offers to resume negotiations.

Secretary of State Antony Blinken spoke at the end of security talks in Seoul, which included Defense Secretary Lloyd Austin and South Korea's foreign and defense ministers. Their first so-called “two plus two” meeting in five years came as President Joe Biden pushes to restore America’s alliances in Asia in the face of challenges from China and North Korea.

“Beijing has an interest, a clear self-interest, in helping to pursue denuclearization of (North Korea) because it is a source of instability. It is a source of danger and obviously a threat to us and our partners,” Blinken told a news conference.

He said Beijing has a critical role to persuade North Korea to denuclearize because most of the North’s external trade goes through China. Blinken stressed that China is obligated by U.N. Security Council resolutions to fully enforce sanctions imposed over North Korea’s nuclear and missile tests.

China, the North’s last major ally and biggest aid benefactor, has long been suspected of avoiding completely implementing sanctions on the North. Some observers say China believes a unified, pro-U.S. Korea would undermine its strategic interests and worries that a humanitarian disaster in North Korea could push swarms of refugees flooding over the countries’ border.

Chinese Foreign Ministry spokesperson Zhao Lijian said Beijing would “continue to play a constructive role” in working toward a political settlement on the Korean Peninsula. Zhao reiterated Thursday that China advocates a “two-track approach” to the issue, whereby the U.S. would offer security guarantees to North Korea in exchange for Pyongyang abandoning its nuclear weapons programs.

“All parties concerned should move in the same direction, work together to manage differences, actively promote dialogue and contacts, and maintain regional peace and stability,” Zhao told reporters at a daily briefing Thursday.

Earlier Thursday, Choe Son Hui, North Korea’s first vice foreign minister, confirmed Blinken’s previous announcement that Washington had reached out to Pyongyang through several channels starting in mid-February, but it hasn’t received any response.

Choe called the U.S. outreach a “time-delaying trick” and said North Korea would discarding offers for talks unless Washington withdraws its hostility. “What has been heard from the U.S. since the emergence of the new regime is only a lunatic theory of ‘threat from North Korea’ and groundless rhetoric about ‘complete denuclearization,’” she said.

Asked about Choe’s statement, Blinken said he’s more interested in the thoughts of U.S. partners while he was making a regional tour. South Korean Foreign Minister Chung Eui-yong said Thursday’s talks dealt with the North Korean statement and its intentions. He said South Korea hopes for the early resumption of U.S.-North Korean talks.

U.S.-led diplomacy focusing on North Korea’s nuclear weapons remains stalemated because of disputes over U.S.-led sanctions. Experts are debating whether the United States and its allies should settle for a deal that would freeze North Korea’s nuclear activities in return for relaxing sanctions to prevent its arsenal from growing.

Earlier this week, the powerful sister of North Korean leader Kim Jong Un warned the United States to “refrain from causing a stink,” while criticizing the U.S.-South Korean drills that her government views as an invasion rehearsal.

Some experts say North Korea may further raise animosities with missile tests to boost its negotiation leverage. North Korea’s moribund economy is hurting because of the pandemic-related border closure that has significantly shrunk its external trade and a spate of natural disasters last summer.

After Thursday’s talks, Blinken, Austin and their South Korean counterparts said in a joint statement that North Korean nuclear and ballistic missile issues are “a priority for the alliance” and reaffirmed a shared commitment to address those issues.

Austin said the U.S. is fully committed to the defense of South Korea, using “the full range of U.S. capabilities, including our extended deterrent.” Blinken slammed North Korea’s human rights record for a second straight day, saying that people in North Korea “continue to suffer widespread and systematic abuses at the hands of a repressive government.”

Later Thursday, Blinken and Austin met South Korean President Moon Jae-in, who said Seoul will continue close cooperation with Washington to achieve complete denuclearization and lasting peace on the Korean Peninsula.

Blinken and Austin are on the first overseas trip by Cabinet-level officials since Biden took office. They visited Japan before coming to Seoul.

South Korean Defense Minister Suh Wook said that during Thursday’s talks the U.S. side stressed the importance of a U.S.-led trilateral security cooperation involving Seoul and Tokyo many times. He said South Korea in principle agrees on the U.S. view. Ties between Seoul and Tokyo have suffered major setbacks in recent years over issues stemming from Japan’s 1910-45 colonization of the Korean Peninsula.

Blinken said Thursday’s talks discussed China’s role, and “we are clear eyed about Beijing’s consistent failure to uphold its commitments.”

“And we spoke about how Beijing’s aggressive and authoritarian behavior are challenging the stability and security prosperity of the Pacific region,” he said. “Beijing’s actions make forging a common approach among our allies all the more important at a time when we’re seeing a rollback of democracy and human rights around the world, including in Burma.”

Beijing has rebuked Blinken's similar remarks in Tokyo, and his renewed criticism came ahead of his first in-person meetings with Chinese counterparts in Alaska on Thursday.

Blinken called for unity among allies, despite Seoul's hesitance to provoke China, its largest economic partner and an ally of North Korea.

"It is more important than ever that we stand together for the values for the interest that unite us," he said.

Blinken will meet senior Chinese officials in Anchorage, Alaska, on his way back to Washington, while Austin will travel on to New Delhi for talks with Indian officials.

China’s ambassador to the United States, Cui Tiankai, said Beijing doesn’t expect the Alaska talks will resolve all the issues between China and the U.S. and “we don’t hold overly high hopes.” Cu still added that he hoped the meeting would be “a start and that the two sides can begin a dialogue process that is candid, constructive and realistic.”