By Jonathan Cheng

SEOUL -- President Donald Trump and his top diplomat hardened the U.S. approach to North Korea, ruling out direct talks and raising the option of a pre-emptive strike in statements that set the stage for a potential clash with Chinese leaders this weekend.

The first-strike threat and the U.S. deployment this month of the beginnings of a South Korean missile-defense system represent a shift in balance expected to provoke Beijing, which is North Korea's top ally.

Secretary of State Rex Tillerson, in Seoul on Friday, slammed Beijing for its opposition to the defense system, which is aimed at protecting South Korea against missile threats from the North.

Mr. Trump chimed in hours later, saying Beijing hasn't done enough to address the threat from Pyongyang, which is closing in on the ability to mount a nuclear warhead on a long-range ballistic missile.

"North Korea is behaving very badly. They have been 'playing' the United States for years. China has done little to help!" Mr. Trump tweeted.

Mr. Tillerson was expected to arrive in Beijing on Saturday for meetings over the weekend with Chinese President Xi Jinping as well as China's foreign minister.

A spokeswoman for China's Foreign Ministry on Friday pointed to China's efforts to promote dialogue between Pyongyang, Washington and Seoul, and declined to comment on the secretary of state's remarks ahead of his arrival.

U.S. relations with China have been rocky since Mr. Trump said he would review the longstanding one-China policy, in which Washington agrees not to extend diplomatic recognition to the government of Taiwan. Mr. Trump later committed to "one China" in a phone call with Mr. Xi in February.

Other issues of contention include China's trade and currency policy and its territorial ambitions in the South China Sea.

But since Mr. Trump took office in January, the most pressing matter has been North Korea. Mr. Trump has launched a White House policy review -- which is continuing -- that includes the possibility of military force or regime change to blunt the country's nuclear-weapons threat, according to people familiar with the process.

North Korea has proceeded with missile tests since the inauguration, including one staged while the U.S. and Japanese leaders were meeting in February and a burst of midrange missiles aimed at Japan this month that landed in waters off the east coast of the Korean Peninsula.

Plans for back-channel talks in New York between government representatives from North Korea and former U.S.officials were scuttled last month after the State Department withdrew visa approvals for Pyongyang's top envoy on U.S. relations, according to people familiar with the matter.

Tougher sanctions remain an option in dealing with Pyongyang, Mr. Tillerson said on Friday. The former oil executive's remarks to reporters in Seoul were his most direct statements on North Korea since he was sworn in last month.

Mr. Tillerson also took aim at what he described as President Barack Obama's inaction on North Korea. "Let me be very clear: The policy of strategic patience has ended," he said.

During last year's presidential campaign, Mr. Trump suggested he would consider a wide range of policies on North Korea, at one point calling leader Kim Jong Un a madman who had to be stopped, and at another point suggesting that the two men talk over hamburgers.

Mr. Tillerson's statements dimmed the prospect that the new administration could pursue a diplomatic strategy.

"Since the policy review is still ongoing, it really locks them into a certain path that I don't think had been fully decided yet," said Jenny Town, assistant director for the U.S.-Korea Institute at Johns Hopkins University's School of Advanced International Studies. "This leaves us no diplomatic off-ramp at a time when tensions are rising in the region."

An emerging hard-line approach puts the U.S. on a collision course with South Korea, where an election on May 9 is expected to bring in a leader who will pursue more engagement with Pyongyang.

"You're going to get a liberal president in South Korea who agrees with the Chinese that a hard-line approach doesn't work," said John Delury, an expert in Chinese and North Korean affairs at Yonsei University in Seoul. "The environment isn't good for them to launch this kind of a suffocation strategy."

Some say the U.S. has little choice but to pursue aharder line.

"This conversation has to be antagonistic, but it has to be now," said Mira Rapp-Hooper, a senior fellow at the Center for a New American Security, a Washington, D.C.-based think tank. "The Trump team may be able to extract some additional efforts from China but whether that is enough to bring enough pain upon the North Korean regime is a completely different question."

Mr. Tillerson, whose China visit comes at the end of a three-nation trip through East Asia, said he plans to raise U.S. concerns about Beijing's opposition to the South Korean missile-defense system, the Terminal High-Altitude Area Defense, or Thaad.

South Koreans have reported dozens of cases of suspected retaliation by Beijing against South Korean companies doing business in China. South Korea received the first components of the Thaad system this month.

Mr. Tillerson said China should be clamping down on the regional threat from its alliesin North Korea rather than targeting South Korea.

"This is not the way for a regional power to help resolve what is a serious threat to everyone," he said, referring to China. "We instead urge China to address the threat that makes Thaad necessary."

South Korea's foreign minister, Yun Byung-se, described China's actions as bullying that would be met with "clarity and resoluteness" by Washington and Seoul.

The Trump administration has raised the prospect of punitive measures against companies in China in response to growing evidence of their support for North Korea's weapons programs.

With regard to sanctions, Mr. Tillerson said there was more that the international community, including China, Russia and "a widening circle of allies," could do to pressure North Korea.

"I don't believe we have ever fully achieved the maximum level of action that can be taken under the U.N. Security Council resolutions," he said. "Weknow other nations could take actions to alter their relationship with North Korea."

He also dismissed the idea of negotiating with North Korea in hopes of freezing its nuclear and missile programs. The country's capabilities are advanced enough that a mere freeze would still leave it with the ability to threaten the U.S.'s allies and military bases in northeast Asia, he said.

"We do not believe the conditions are ripe to engage in any talks at this time," Mr. Tillerson said. "I'm not sure if we would be willing to freeze with circumstances where they exist today."

Mr. Delury, the Yonsei professor and an advocate of outreach, noted that the Bill Clinton and George W. Bush administrations started with a more hawkish approach to North Korea before shifting to engagement toward the end of their tenures.

"They're going to have to do another rethink and realize that this didn't work, and that maybe we do have to talk to theseguys," Mr. Delury said.

--Felicia Schwartz contributed to this article.

Write to Jonathan Cheng at jonathan.cheng@wsj.com

(END) Dow Jones Newswires

March 17, 2017 19:19 ET (23:19 GMT)

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