WASHINGTON (AFP) - US President Barack Obama on Tuesday urged China to play by the "same rules" in the global economy but voiced hope for cooperation in a key introductory meeting with leader-in-waiting Xi Jinping.

China's vice president, who is expected to take the helm next year, largely focused on the positive on his closely watched US visit. He pledged in general terms that China would improve its widely criticized record on human rights.

Xi made the rounds in Washington as Tibetans and others staged noisy protests outside most venues. At the Pentagon, he was given a rare honor ceremony with a 19-gun salute and booming cannons.

Obama, welcoming Xi to the Oval Office, said that Washington welcomed a "prosperous" China and praised its "extraordinary development over the last two decades," but stressed that power came with "increased responsibilities."

"We want to work with China to make sure that everybody is working by the same rules of the road when it comes to the world economic system," Obama said alongside a relaxed-looking Xi, as senior aides and translators stood by.

"That includes ensuring that there is a balanced trading flow not only between the United States and China but around the world," Obama said.

The US leader also brought up concerns about human rights, saying Washington would "continue to emphasize what we believe is the importance of realizing the aspirations and rights of all people."

Speaking later at a luncheon for Xi at the State Department, Vice President Joe Biden sharply criticized China's decision to join Russia in vetoing a UN resolution condemning violence in Syria, as well as Beijing's rights record.

"We have been clear about our concern over the areas in which, from our perspective, conditions in China have deteriorated and about the plight of several very prominent individuals. We appreciate your response," Biden said.

Xi responded that China has made "tremendous and well-recognized achievements" in human rights but added: "There is always room for improvement."

"We will, in light of China's national conditions, continue to take concrete and effective policies and measures to promote social fairness, justice and harmony and push forward China's course of human rights," Xi said.

Chinese President Hu Jintao made similar remarks in Washington last year, and acknowledged China does not share Western ideas about human rights, believing its "national" characteristics must be taken into account.

The Obama administration has spent months planning the visit by Xi, who is expected to succeed Hu next year and could serve as president for a full decade in which many experts believe that China will grow at breakneck speed.

But China is already in the firing line ahead of US elections in November, particularly on economic issues. US lawmakers accuse Beijing of keeping the value of its currency unfairly low to fuel inexpensive exports that have turned China into a manufacturing superpower.

At the luncheon, Xi said the United States and China should "should address each other's economic and trade concerns through dialogue and consultation, not protectionism, and uphold the mutually beneficial pattern of China-US economic relations and trade."

China has let its yuan appreciate since mid-2010 in response to concerns over inflation. But the United States wants China to do more and to take action in other areas including protection of US intellectual property.

As he held talks at the White House, dozens of impassioned pro-Tibet activists outside waved flags and chanted "China lies, Tibetans die" and "Xi, Tibet will be free!"

China has stepped up detentions of government critics since last month and has recently imposed what residents say is virtual martial law in Tibetan areas after a wave of self-immolation protests against Beijing's rule.

The wife of Gao Zhisheng, a lawyer who has defended some of China's most vulnerable people including coal miners and underground Christians, voiced fear that her husband may be dead. He was arrested in February 2009 and little has been heard from him since.

"The government has lied to the family so many times in the past few years.

They laugh at and play games with the family," Geng He told AFP before testifying Tuesday at the US government's Congressional-Executive Commission on China.

Author Yu Jie, who fled to the United States last month after what he said was torture by Chinese police, pressed for Obama to take a firmer approach on human rights.

"The Chinese Communist Party remains a tiger that will bite," Yu wrote in an opinion piece in The Washington Post.

Xi heads Wednesday to Iowa, where he will meet Midwesterners from his first trip to the United States in 1985, before heading to California where he is likely to watch a Los Angeles Lakers basketball game.