WASHINGTON » President Barack Obama and Chinese President Xi Jinping pledged today to cooperate to confront the North Korean nuclear threat while working to narrow persistent differences over cybersecurity, human rights and maritime conflicts.

Obama, opening a global nuclear security summit near the White House, also joined leaders of Japan and South Korea in calling for further joint steps to deter North Korea. The display of diplomatic unity came as world leaders sought to ramp up pressure on the insular country’s government following worrisome nuclear provocations.

“President Xi and I are both committed to the denuclearization of the Korean Peninsula,” Obama said as he and Xi sat down for a meeting on the sidelines of the summit. “We’re going to discuss how we can discourage actions like nuclear missile tests that escalate tensions and violate international obligations.”

The U.S. has long urged China, the North’s traditional ally, to take a more forceful role in pressing North Korea to give up its nuclear weapons program. The Obama administration was encouraged by China’s role in passing new stringent U.N. sanctions punishing the North, and was urging Beijing to implement those sanctions dutifully.

Yet in a nod to deep tensions between the U.S. and China, Obama said he planned to raise thornier issues during their meeting as well — including the disputed South China Sea, where China is asserting territorial claims despite competing claims by its neighbors. Parroting careful diplomatic language long-preferred by Beijing, Obama said the U.S. welcomes China’s peaceful rise to prosperity.

“I very much appreciate President Xi’s willingness to have conversations on these issues in a constructive way,” Obama said.

Xi, addressing reporters through a translator, said the two economic powers would keep deepening ties on trade, law enforcement and climate change. He said the U.S. and China must work together promote peace in light of the rising global terror threat.

“China and the U.S. have a responsibility to work together,” Xi said. As for their “disputes and disagreements,” the Chinese leader said the two sides could “seek active solutions through dialogue and consultation.”

Long at odds over human rights, the U.S. and China in recent years have sparred regularly over China’s move to building artificial islands and military facilities in the disputed South China Sea. Japan and South Korea are similarly alarmed about China’s territorial designs on the East China Sea.

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. China accuses the U.S. of stoking tensions by sending military ships and planes through the South China Sea on freedom of navigation maneuvers.

Still, it was concerns about North Korea’s recent nuclear test and rocket launch drove the agenda on the first day of the two-day summit, Obama’s last major chance to focus global attention on disparate nuclear security threats before his presidency ends early next year.

In a rare joint meeting with Japanese Prime Minister Shinzo Abe and South Korean President Park Geun-hye, Obama said the U.S. was united with its allies because “we recognize that our security is linked.” All three leaders urged the world community to stand firmly behind the sanctions.

Park, whose country has been repeatedly threatened by Pyongyang, warned North Korea that the global community “will by no means” condone its provocations. In recent weeks, North Korea has warned it could strike South Korea’s presidential palace or even the U.S. mainland, and its propaganda outlet posted a video depicting a nuclear attack on Washington.

“Should it choose to undertake yet another provocation, it is certain to find itself facing even tougher sanctions and isolation,” Park said of Pyongyang.

Though leaders spent much of today focused on North Korea, the overriding focus of this year’s summit centered on the Islamic State group and other extremists who security officials warn could someday get their hands on nuclear materials.

As the summit opened, 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.

Obama also planned to meet today with French President Francois Hollande, amid steep concerns about terrorism in Europe following Islamic State-linked attacks in Paris and Brussels. The summit continues on Friday with a special session focused on preventing IS and other extremists from obtaining nuclear materials and attacking urban areas.

Associated Press writers Kevin Freking and Darlene Superville contributed to this report.