President Barack Obama will be meeting with Asian leaders in Washington this week as fears grow that long-smoldering tensions on the Korean Peninsula and in the South China Sea risk flaring into conflict.
World leaders, including those from China, Japan and South Korea, will be in town for a summit hosted by Obama on nuclear security - the final round in the U.S. president's drive for international action to stop materials that could be used for an atomic weapon or dirty bomb from getting into terrorist hands.
But other pressing security issues will be up for discussion on the sidelines of the two-day gathering that starts Thursday.
Obama will on Thursday meet separately with China's President Xi Jinping at a time when frictions between the two world powers over China's island-building in strategic waters are growing and look set to intensify with an upcoming ruling from an international tribunal on Beijing's sweeping territorial claims.
The U.S. president is also meeting with Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye. Washington is looking for an elusive unity between its core allies in Asia as threats from North Korea reach fever-pitch after Pyongyang was stung with tough sanctions in response to its recent nuclear test and rocket launch.
Obama will be urging China to implement the U.N. sanctions it signed up to for use against North Korea, its traditional ally. For his part, Xi will want the U.S. to restart negotiations with the authoritarian government of Kim Jong Un, which has been touting progress in miniaturizing nuclear devices and missile technology that could directly threaten America.
Deputy Secretary of State Antony Blinken said Tuesday that if North Korea keeps advancing its weapons programs, the U.S. will be compelled to take defensive measures that China will not like, such as the deployment of a missile defense system being discussed with South Korea. Beijing is concerned the system's radar could cover Chinese territory.
"The bottom line remains that as long as North Korea continues in this direction, advancing its nuclear program, advancing its missile program, we are going to have to take these steps to defend ourselves and to defend our partners," Blinken told a Washington think tank.
With Obama's presidency in its final year, there's uncertainty among Asian nations on what the next administration will portend. Republican presidential frontrunner Donald Trump is calling for Japan and South Korea to pay more for U.S. military protection, and is advocating a tougher trade policy toward China.
During his seven years in office, Obama has deepened engagement with Asia, despite the huge distraction of chaos in the Middle East. The U.S. and China have cooperated on issues like climate change and nuclear security, even as their strategic rivalry has grown. The U.S. is a major player in China's fast-growing nuclear industry, and this month, the U.S. and China opened a center in Beijing to train technicians and scientists from across the Asia-Pacific on nuclear security.
But when Obama and Xi meet, the hottest topic will be the most divisive one: China's bold pursuit of its sweeping territorial claims in the South China Sea.
China has reclaimed more than 3,000 acres of land in the past two years near sea lanes crucial for world trade. On these artificial islands, Beijing has installed airstrips and other military facilities that U.S. intelligence assesses will enable China to project offensive military power in the region by early next year.
Despite conflicting territorial claims from five other Asian governments, China contends it has a historic right to most of the South China Sea and maintains the U.S. has no business there. It accuses the U.S. of stoking tensions by sending military ships and planes through the area on freedom of navigation maneuvers.
"Washington should know that the more provocative moves it makes against China, the more counter-measures Beijing will take. Such an undesirable cycle may push both sides nearer confrontation and cause both to prepare for the worst-case scenario, potentially making it self-fulfilling," the U.S. edition of the state-supported China Daily said in a recent editorial.
The stakes are set to rise by mid-year when an international arbitration body is set to rule on a case brought by the Philippines challenging the legal basis of the nine-dash line - Beijing's rough demarcation of its claims.
If the Hague-based tribunal rules in the Philippines' favor, as most experts anticipate, it could undermine China's insistence that its stance is consistent with international law. China has refused to participate in the arbitration and says it will ignore the ruling, but a growing number of countries say both parties should be bound by it.
Jeffrey Bader, Obama's former principal advisor on Asia, wrote in a commentary ahead of the summit that there's concern in Washington and the region about how China might react to the ruling, and whether it will militarily challenge Filipino territorial claims. He said that as the Philippines is a U.S. ally, Obama "may warn Xi of the risks of escalation."
The last time Xi visited Washington, in September, he publicly said that China did not intend to pursue militarization in the Spratly islands where most of land reclamation has happened - a statement that U.S. officials remind Beijing of at every opportunity. But in recent weeks, China has reportedly positioned more military equipment on disputed islands in the South China Sea.