A large-scale US-South Korean naval exercise that begins Sunday in the Sea of Japan near North Korea has inflamed tensions in what has been for more than half a century a dangerous flashpoint in North East Asia. Both North Korea and China have voiced their opposition.

The war games codenamed “Invincible Spirit” are specifically aimed against North Korea over its alleged sinking of the South Korean warship, the Cheonan, in March with the loss of 46 sailors. South Korea and the US have been seeking to penalise North Korea after a South Korean investigation concluded that North Korea was responsible for the attack. Pyongyang has denied any involvement.

The exercise involves around 20 South Korean and US warships, including the nuclear-powered aircraft carrier USS George Washington, 200 aircraft, including advanced F-22 fighters, and 8,000 military personnel. This massive show of force far exceeds what is required to deal with any threat from the North Korean navy and has been denounced by Pyongyang as a “reckless provocation.”

The South Korean media initially reported that the exercise would take place in the Yellow Sea—that is, to the west of the Korean Peninsula and close to the Chinese mainland. Beijing, however, reacted angrily to what it regarded as a direct security threat. A Chinese foreign ministry spokesman last week declared: “We resolutely oppose any activities in the Yellow Sea that may threaten China’s security.”

Japan injected itself into the dispute, announcing that four Japanese observers will participate in Invincible Spirit, on board the USS George Washington. It is the first time that military officers of Japan, which maintained a brutal colonial rule over Korea from 1895 to 1945, have taken part in a US-South Korean military exercise.

In a further provocation, the US-led United Nations Command formally notified North Korea of plans to hold another joint US-South Korean military exercise at unspecified locations from August 16 to August 26.

An editorial in the China Daily on July 13 stated: “The public outcry in China will turn stronger if the US decides that its nuclear-powered aircraft carrier USS George Washington is to participate in the exercise. The vessel’s likely presence, whose combat radius can reach the nation’s eastern coast, is nothing but a provocative action aimed at China’s doorsteps.”

Commenting in the People’s Daily, Chinese general Luo Yuan exclaimed: “If the United States were in China’s shoes, would it allow China to stage military exercises near its western and eastern coasts?” He warned that the two purposes of the US-South Korea joint exercise, “strategic reconnaissance and testing initial combat plans, will pose a threat to China.”

China held a live-fire naval exercise in the East China Sea—to the south of the Korean Peninsula—from June 30 to July 5, involving a large number of fighters. As the US announced the planned exercise with South Korea last Tuesday, Chinese state television broadcast footage from more recent exercises in the Yellow Sea, saying that their purpose was to counter “long-distance attacks”.

Far from backing off, State Department spokesman P.J. Crowley declared last week that other US-South Korean drills planned this year would eventually involve the Yellow Sea, regardless of Chinese opposition. “Obviously [the Chinese] are a regional power and a country…whose opinion we respect and consider,” he said. “But this is a matter of our ability to exercise in open seas, international waters. Those determinations are made by us and us alone.”

US Secretary of Defense Robert Gates and Secretary of State Hillary Clinton were in South Korea last Tuesday to meet with their South Korean counterparts. As well as announcing the joint naval exercise, Gates and Clinton also visited the demilitarised zone between North and South Korea. It was the first time that two top US cabinet officials, responsible for national security policy, had toured the DMZ at the same time.

The top uniformed officer in the US military, Admiral Michael Mullen, chairman of the Joint Chiefs of Staff, was in Seoul for talks with his South Korean counterparts. US commanders will retain operational control of their joint military forces in South Korea until at least December 2015. Previously, the US military was scheduled to hand over operational command in 2012.

Gates declared the visits were intended “to send a strong signal to the North, to the region and to the world that our commitment to South Korea’s security is steadfast.” In an indirect reference to China, he added: “In fact, our military alliance has never been stronger and should deter any potential aggressor.” He also foreshadowed joint exercises in the Yellow Sea.

Clinton announced new sanctions against North Korea. Although providing no details, she said that the sanctions would freeze more North Korean overseas assets, prevent additional individuals from traveling abroad and tighten international bank transactions involving Pyongyang. She also pledged that the US would provide “a stalwart defense” of South Korea.

The tough US stance in South Korea is in part a response to the US failure to obtain a UN Security Council resolution condemning North Korea over the Cheonan sinking and imposing new penalties. Much to Washington’s annoyance, China refused to accept the findings of the South Korean investigation blaming North Korea or to back a UN resolution. In the end, the UN Security Council only issued a presidential statement in early July condemning the sinking but without naming North Korea as the attacker.

In an indication of the underlying tensions between the US and China, President Obama made an unusually blunt criticism of China at the G20 summit in June, accusing Chinese President Hu Jintao of “willful blindness” over North Korea’s alleged provocations. While professing to understand China’s concerns about the Korean peninsula, Obama said: “My hope is that President Hu will recognise that this is an example of Pyongyang going over the line in ways that just have to be spoken about, seriously.”

The differences between the US and China over North Korea are part of their broader rivalry throughout Asia and internationally. The economic rise and continued growth of China threaten to eclipse the US in North East Asia where major US allies—Japan, South Korea and Taiwan—are all heavily dependent on trade with China. The US is responding by flexing its military muscles, reminding the same countries of their military dependence on Washington.

The frictions were also evident at the Association of South East Asian Nations (ASEAN) Regional Forum Thursday and Friday in Vietnam. Clinton, who has championed a more aggressive US stance in Asia, told a meeting with ASEAN leaders: “The American future is intimately tied to that of the Asia-Pacific. The United States is a Pacific nation and we are committed to being an active partner with the ASEAN and with all of you.” Washington achieved a small diplomatic victory, securing entry into the East Asian Summit (ASEAN plus China, Japan and South Korea).

Clinton called for North Korea to be condemned over the Cheonan sinking, declaring that Pyongyang was conducting a “campaign of provocative, dangerous behavior,” a description that would seem to apply as readily to American policy in the region. As in the case of the UN, US pressure was not sufficient to overcome Chinese opposition, and the ASEAN statement was relatively mild.

The North Korean representative at the Hanoi meeting, Ri Tong-il, vehemently denounced the upcoming military exercises. “Such a move presents a grave threat to the peace and security not only to the Korean peninsula, but to the region,” he said, adding that there would be “a physical response.”

“If the US is really interested in the denuclearisation of the Korean peninsula,” he said, “it should halt the military exercises and sanctions that destroy the mood for dialogue.”

Clinton used the forum to press China on several fronts: lashing out at Burma, a close Chinese ally, over human rights, and pressing for free navigation in the South China Sea which Beijing regards as particularly sensitive to its strategic interests. The bulk of China’s oil shipments from the Middle East and Africa pass through the area.

The US intervention in the South China Sea controversy is particularly provocative. China, Vietnam, the Philippines and Malaysia all have claims to all or part of the Spratlys, a chain of small reefs and islets in waters that are both strategically located and believed to hold undersea oil reserves. Clinton called for international resolution of the dispute, effectively siding with Vietnam against China. The New York Times commented, “Though presented as an offer to help ease tensions, the stance amounts to a sharp rebuke to China.”

The Times account continued: “The administration’s decision to get involved appeared to catch China flat-footed and angered its foreign minister, Yang Jiechi, at a time when the country is already on edge over naval exercises the United States and South Korea will hold starting this weekend. Twelve of the 27 countries at the security meeting spoke out in favor of a new approach to the South China Sea, prompting Mr. Yang to observe that the American effort seemed orchestrated.”

On the first day of the ASEAN meeting, the Obama administration announced that it would resume military-to-military relations with Kopassus, the special forces deployed by the Indonesian military junta to suppress both domestic opposition and separatist movements. US officials said the ban was no longer needed because Indonesia had become a democracy.

But the Washington Post adduced another reason, writing: “The Obama administration’s announcement Thursday that it will resume relations with Indonesia’s special forces, despite the unit’s history of alleged atrocities and assassinations, is the most significant move yet by the United States to strengthen ties in East Asia as a hedge against China’s rise. The push comes at the same time that the administration’s tone with China has turned tougher, especially on the nettlesome issue of human rights. In recent speeches and interactions with Chinese authorities, the administration has abandoned an earlier approach of patience and quiet engagement.”