U.S. President Barack Obama and his Russian counterpart Vladimir Putin met briefly Monday in Beijing on the sidelines of an Asia-Pacific summit, a senior U.S. official said.

The two leaders, who have been engaged for months in a standoff over the crisis in Ukraine, "only had a brief encounter where they didn't have time to cover issues," the official said on condition of anonymity.

President Barack Obama on Monday dismissed North Korea's release of two imprisoned Americans as "small gestures", saying nuclear-armed Pyongyang must change its attitude on atomic weapons if it wants improved ties.

"We have been consistent in saying that when and if North Korea becomes serious about de-nuclearization on the peninsula and is prepared to have a conversation around that topic, then the United States is going to be very open to try to arrive at a solution," Obama told reporters in Beijing.

The leaders of China and Japan held an ice-breaking summit Monday after two years of dangerous animosity, as world leaders including Barack Obama gathered for an Asia-Pacific meeting spotlighting intensifying big-power rivalries.

Xi Jinping and Shinzo Abe met in Beijing's Great Hall of the People in what the Japanese prime minister said was a "first step" towards repairing the fractured relationship between the world's second- and third-largest economies.

President Barack Obama announced a deal Monday to extend visas for Chinese visitors to the United States for up to a decade, insisting he wants China "to do well" despite simmering tensions between the world's two largest economies.

"The United States welcomes the rise of a prosperous, peaceful and stable China," Obama said in a speech at the Asia-Pacific Economic Cooperation (APEC) summit in Beijing.

U.S. Secretary of State John Kerry arrived Sunday in Oman to seek a breakthrough in nuclear talks with Iran, with domestic pressures weighing heavily on hopes for a deal.

Kerry will meet Iran's Foreign Minister Mohammad Javad Zarif during the day to try to close substantial gaps that have blocked the latest efforts to turn an interim agreement into a comprehensive long-term settlement.

North Korea's surprise release of two jailed American citizens is further evidence that Pyongyang is genuinely rattled by moves at the United Nations to charge its leadership with crimes against humanity, analysts said Sunday.

The release of Kenneth Bae and Matthew Miller came days after an EU-Japan draft resolution -- co-sponsored by 48 countries -- was submitted to a U.N. General Assembly committee, urging the Security Council to refer the Pyongyang regime to the International Criminal Court (ICC).

President Barack Obama headed for China Sunday on a trip that will focus on Washington's often tense relations with the country, and will also see the president visit Myanmar and Australia.

The China stop will be dominated by Obama's meeting with Chinese President Xi Jinping in Beijing, where the White House said it expects "candid and in-depth conversations."

Emboldened by Tuesday's stunning midterm rout of Democrats, the Tea Party movement promises a clash with U.S. President Barack Obama, but an equally consequential battle looms between far-right lawmakers and their Republican leaders.

Several conservatives backed by the small-government, anti-tax movement who romped to election victory after campaigning on pledges to repeal or defund the controversial Affordable Care Act, scrap government departments like the Environmental Protection Agency, and fight Obama tooth and nail over funding government.

U.S. President Barack Obama told the world Friday to remember lessons from the emotional fall of the Berlin Wall 25 years ago, particularly in light of "Russia's actions against Ukraine."

Berlin kicked off celebrations Friday of the 25th anniversary of the fall of the wall, which culminate Sunday with a party to mark the historic event which led to German reunification.

President Barack Obama plans to nominate veteran New York federal prosecutor Loretta Lynch to succeed Eric Holder as U.S. attorney general, the White House said Friday.

If confirmed by the Senate, Lynch would be the first African-American woman to serve as the nation's top law enforcement officer.