BEIJING — U.S. Secretary of State John Kerry warned Wednesday that if China failed to do more to curb North Korea's enhanced nuclear capacity, Washington would take steps that China has strongly opposed, including deploying defense systems to protect U.S. allies in Asia.
"This is a threat the United States must take extremely seriously," Kerry said of North Korea's growing nuclear arsenal at a news conference with the Chinese foreign minister, Wang Yi. "The United States will take all necessary steps to protect our people and allies. We don't want to heighten security tensions. But we won't walk away from any options."
Kerry adopted the tough tone after nearly five hours of talks with Wang that were dominated by North Korea and what the United States and China, a treaty ally of the North, should do in the aftermath of its fourth nuclear test.
The secretary was referring to the deployment of a missile defense system to South Korea that has been under discussion for some time but that the South, a U.S. ally, has resisted because of China's opposition.
But after the North Korean test on Jan. 6, the South's president, Park Geun-hye, said she would consider accepting the missile system — called THAAD, for Terminal High-Altitude Area Defense — to better cope with the North's growing nuclear and missile threats.
China agreed during the talks Wednesday to new U.N. sanctions against the North, and negotiations on their content will proceed in the coming days, Wang said. But these new sanctions "must not provoke new tensions," he said.
A draft of new sanctions was sent to China about 10 days ago, but by the time Kerry arrived in Beijing, China had not responded in substance, U.S. officials said.
Suggesting that the Obama administration was evincing a little too much concern about the North Korean nuclear test, and that Washington's attention would soon drift away, Wang said that China "will not be swayed by specific events or the temporary mood of the moment."
Wang stuck to a basic theme, that China's preference is the reconvening of talks on North Korea. "Sanctions are not an end in themselves," he said.
Kerry made clear that the United States' position was that China, North Korea's biggest trading partner, needed to use its leverage and what he called its "connections" with the country to pressure it to give up its nuclear arsenal.
Washington would like China to curb exports of oil, including aviation fuel, that help keep the bare-bones North Korean economy afloat. It has also asked China to crack down on its banks and businesses that give the North access to foreign exchange.
A bill calling for sanctions against Chinese entities that help North Korea in its military programs, criminal activities and money laundering recently passed with strong support in the House of Representatives.
As part of his attempt to persuade Beijing, Kerry used the example of the recent Iran deal: The restrictions on Iran's banks and financial institutions to conduct transactions abroad helped bring that country to the negotiating table over its nuclear program, a feat that Kerry led and that China supported, along with Russia.
Kerry used the news conference to publicly call on China to take similar actions against North Korea and to create another "united front."
"With all due respect, more significant and impactful sanctions were put against Iran, which did not have nuclear weapons, than against North Korea, which does," Kerry said.
The secretary faces a tough sell. President Xi Jinping of China made a decision last year that it was better for China to have a friendly nuclear-armed North Korea on its border than a hostile nuclear-armed North Korea, Chinese analysts have said.
"For China, the worst-case scenario is you push North Korea over to become an enemy with nuclear weapons," said Zhang Baohui, director of the Center for Asian Pacific Studies at Lingnan University in Hong Kong. "I think China has decided to tolerate North Korea as a nuclear state."
Xi sent a top lieutenant, Liu Yunshan, a member of the Standing Committee of the Politburo, to the North Korean capital, Pyongyang, in October to attend a military parade and to deliver a personal letter from Xi to the North's leader, Kim Jong Un.
Nevertheless, Zhang said, China has urged North Korea to denuclearize. And the North's detonation of a nuclear device on Jan. 6 was a way of telling Beijing that it could not dictate the country's foreign policy, Zhang said.
Chinese officials have told their U.S. counterparts that they were not informed of the timing of the test and that it came as a surprise.
China has accused Washington of using the North Korean nuclear tests as an excuse to deploy the missile defense system in South Korea.
"The THAAD has nothing to do with North Korea. It is simply the U.S. technically trying to deter China and Russia with these missiles and strategically alienating South Korea from China," said Wang Junsheng, a research fellow on Northeast Asia at the Chinese Academy of Social Sciences.