In talks yesterday in Beijing, US Secretary of State John Kerry threatened to escalate the American military build-up in Asia unless the Chinese government agreed to draconian new economic measures against North Korea over its latest nuclear test.

At a news conference with Chinese Foreign Minister Wang Yi, Kerry declared that the US took North Korea’s nuclear weapons “extremely seriously.” He warned: “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.”

Following North Korea’s detonation of a fourth nuclear device on January 6, the US and South Korea said discussions had begun over stationing “strategic assets” on the Korean Peninsula—in other words, bombers, submarines or warships capable of launching a nuclear attack. To underscore the warning, the Pentagon flew a nuclear-capable B-52 strategic bomber to South Korea four days later.

As Beijing is well aware, the US military build-up is not primarily aimed at North Korea and its limited stockpile of nuclear weapons. Rather it is targeted against China itself, as part of the Obama administration’s “pivot to Asia” over the past five years. Kerry’s visit came just days after the Centre for Strategic and International Studies (CSIS) released a comprehensive study commissioned by the Pentagon calling for an accelerated US military expansion in Asia to counter China.

The rather blunt diplomatic comments by Kerry and Wang at yesterday’s press conference obviously masked more rancorous exchanges behind closed doors. Journalists waited around as the pair’s meeting dragged out for nearly five hours. As the Washington Post noted, when they finally appeared, “tension [was] written across their faces.”

Kerry had already made clear, before his visit, that he intended to confront the Chinese leadership over North Korea. Following Pyongyang’s nuclear test, he declared that China’s “particular approach” to North Korea had “not worked” and warned “we cannot continue business as usual.” A senior State Department official told the media earlier this week that Kerry would not only press Chinese officials for a tough UN resolution but for “what China on a unilateral basis, as North Korea’s lifeline, as North Korea’s patron, will choose to do.”

Yesterday Kerry outlined the sweeping character of the sanctions demanded by the US, saying: “There are certain goods and services that flow between North Korea and China; there are movements of ships, ports, so forth; aviation is an area and a sector of concern; various resource exchanges, whether it’s coal or fuel—all of these areas where there are border customs.”

Washington is demanding that Beijing choke off North Korea’s only access to vital supplies such as oil and aviation fuel, severely limit trade and block its already restricted connections to the global financial system. Such measures threaten to precipitate an economic collapse in North Korea and a severe political crisis for the fragile North Korean regime.

The Chinese leadership had flatly refused to impose such a blockade, fearing that a political implosion in Pyongyang would send a flood of refugees into northern China and open the door for Washington to engineer a pro-US regime on China’s doorstep. While condemning North Korea’s nuclear test, Foreign Minister Wang declared that “sanctions are not an end in themselves” and urged a return to “the path of negotiation and consultation.” He insisted any UN resolution “should not provoke new tension in the situation, [or] destabilise the Korean Peninsula.”

Beijing is the sponsor of the so-called six party talks involving the US, China, Japan, the two Koreas and Russia. An international agreement on North Korea’s nuclear programs broke down in 2008 after the Bush administration unilaterally demanded a tougher inspection regime. The Obama administration has made no attempt to revive the negotiations, insisting instead that North Korea commit to giving up its nuclear weapons prior to any talks.

Washington has exploited the ongoing tensions on the Korean Peninsula as the pretext for strengthening its military presence. After the previous North Korean nuclear test in 2013, the Pentagon announced the expansion of its anti-ballistic missile system in Asia with the stationing of a second THAAD battery in Japan. The US is now pushing for South Korea to accept a THAAD installation. These anti-ballistic missile systems are integral to the US preparations for war with China.

Keeping up the pressure on Beijing, Kerry emphasised that it was “good to agree on the goal, but it’s not enough to agree on the goal... We are looking forward to working with China ... to achieve an understanding about the strong resolution that introduces significant new measures to curtail North Korea’s ability to advance its prescribed nuclear and ballistic missile programs.”

While North Korea was on top of the agenda, Kerry also again demanded an end to China’s land reclamation activities and “militarisation” in the South China Sea. He insisted that the US did not take sides on the territorial disputes between China and its neighbours. He advocated their settlement “under the Law of the Sea, arbitration, rule of law, direct bilateral negotiation.”

In reality, Washington, which has not ratified the UN Convention on the Law of the Sea, has directly challenged China’s maritime claims. Last October, the Pentagon deliberately sent the guided missile destroyer, the USS Lassen, within the 12-nautical-mile territorial limit surrounding a Chinese-administered islet.

Wang declared that “the South China Sea Islands have historically been China’s territory” that China has a right to protect. He said facilities for self-defence were not the same as militarisation. “If one equates such a right to militarisation, then the South China Sea has been militarised long ago, and mind you, China was not the first party that started the militarisation,” he said, a reference to the actions of Vietnam and the Philippines.

Kerry and Wang made repeated pro forma references to the need for greater collaboration between the United States and China to ensure peace and stability. The meeting, however, signalled deepening tensions between the two countries as the Obama administration steps up its “pivot,” accompanied by a distinct lack of cooperation on potentially-explosive issues.