WASHINGTON -- In the face of mounting threats from North Korea, President Barack Obama on Thursday urged closer security ties among America's chief allies in Asia and increased co-operation with strategic rival China to discourage Pyongyang from further advances in nuclear weapons.
As world leaders gathered for a nuclear security summit, Obama first met with Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye. Together, they warned North Korea would face even tougher sanctions and more isolation if provoked again with nuclear and missile tests.
Then Obama met Chinese President Xi Jinping and both called for North Korea to give up its nuclear weapons. China also agreed to implement in full the latest economic restrictions imposed by the U.N. Security Council against Pyongyang.
More than 50 governments and international organizations are attending the two-day summit on preventing nuclear terrorism -- the last in a series of global meetings Obama has championed on the issue. The risk posed by the Islamic State group tops this year's agenda but concerns about North Korea are also commanding focus.
"Of great importance to both of us is North Korea's pursuit of nuclear weapons, which threatens the security and stability of the region. President Xi and I are both committed to the denuclearization of the Korean Peninsula," Obama said at the start of his meeting with Xi.
"China and the U.S. have a responsibility to work together," Xi said in his comments made to reporters through an interpreter. As for their "disputes and disagreements," the Chinese leader said the two sides could "seek active solutions through dialogue and consultation."
North Korea's fourth nuclear test in January, followed by a space a launch in February, have heralded more convergence among often-fractious powers in East Asia -- at least on the need to press the government of Kim Jong Un toward disarming.
Japan and South Korea have persuasive reasons to get along. They both host U.S. forces and are both in range of North Korean missiles. But their relations have been plagued by historical differences that date back to Japan's colonial occupation of Korea in the first half of the 20th century and its military's use of sex slaves during World War II.
But those tensions have eased some. Abe said North Korea nuclear and missile capability is a "direct and grave threat" to them all.
"Should it choose to undertake yet another provocation, it is certain to find itself facing even tougher sanctions and isolation," Park said of Pyongyang.
Young leader Kim Jong Un has also alienated the North's traditional benefactor and main trading partner, China. The U.S. has long urged Beijing to take a more forceful role in pressing North Korea, and Chinese Vice Foreign Minister Zheng Zeguang said after the Obama-Xi meeting that the two sides agreed the new U.N. resolution "should be implemented in full and in its entirety."
The U.S. and China also released joint statements vowing robust collaboration to improve nuclear security and to implement a global climate change deal, and reported progress on the issue of cyber security.
But they were at stark odds in other areas.
According to Zheng, Xi told Obama that China was "firmly opposed" to the U.S. deploying a new missile defence system in South Korea, saying it was against China's national security interests and would affect the strategic balance in the region.
The U.S. and Seoul are considering that deployment to counter the threat from the North. China contends the system would also give the U.S. radar coverage over Chinese territory. Russia opposes it as well.
Washington has also opposed China's move to build artificial islands and military facilities in the disputed South China Sea. Japan and South Korea are similiarly concerned about China's military build-up and assertive actions in the region's disputed waters.
Tensions appear set to intensify with an upcoming ruling from an international tribunal that could challenge the legal basis of some of Beijing's sweeping territorial claims. The U.S. has supported the right of its ally, the Philippines, to submit the case and says the ruling should be binding on both parties, although China has boycotted the proceedings and says it will ignore it.
Xi told Obama that the South China Sea islands -- claimed by several other Asian governments -- have been China's territory since ancient times and it has the right to defend its territorial sovereignty and maritime rights, Zhang said.
Obama also met Thursday with French President Francois Hollande, amid steep concerns about terrorism in Europe following Islamic State-linked attacks in Paris and Brussels. The nuclear security summit continues on Friday with a special session focused on preventing IS and other extremists from obtaining nuclear materials and attacking urban areas.
On Thursday, the U.S. said a strengthened nuclear security agreement among nations was finally set to take force following ratification by a critical mass of countries. The stricter rules include new criminal penalties for smuggling nuclear material and expanded requirements for securing materials and nuclear facilities worldwide, and are intended to reduce the likelihood of terrorists getting their hands on ingredients for a bomb.
The United States says it's making progress in reducing its stockpiles of highly enriched uranium. The White House says it's declassifying and publicly releasing a national inventory of highly enriched uranium for the first time since 1996. As of late 2013, the U.S. had 586 metric tons of highly enriched uranium. That's a drop from the 741 metric tons the U.S. had in 1996.
Fissile materials like highly enriched uranium and separated plutonium can be used to make nuclear bombs.
Associated Press writers Kevin Freking and Darlene Superville contributed to this report.
