By Steve Holland and Jeff Mason
WASHINGTON (Reuters) - President Barack Obama pressed for bold, swift sanctions on Iran on Tuesday but acknowledged China has concerns about the economic impact and said negotiations are difficult.
Ending an unprecedented 47-nation nuclear security summit, Obama won pledges from world leaders to take joint action to prevent terrorist groups from getting nuclear weapons, steps he said will make the United States and the world safer.
"Today is a testament of what is possible when nations come together in a spirit of partnership to embrace our shared responsibility and confront a shared challenge," Obama said.
Iran's nuclear standoff with the West cast a shadow over the summit, and it was clear that some major hurdles remain on the road to imposing a new round of U.N. sanctions on Iran over its alleged pursuit of nuclear weapons.
A day after discussing Iran with Chinese President Hu Jintao, Obama expressed gratitude that China had agreed to help negotiate a new U.N. sanctions resolution on Iran but said Beijing still has concerns about sanctions.
He said he had argued to Hu that there must be consequences for Iran's violation of its international obligations. Tehran denies trying to develop an atomic weapon, saying it wants peaceful nuclear power for electricity.
"The Chinese are obviously concerned about what ramifications this might have on the economy generally," Obama said. "Iran is an oil-producing state."
Obama on March 30 said he hoped to get a new sanctions resolution ready within weeks.
He declined to repeat the timetable on Tuesday but said he did not want a long, drawn-out process that takes months, and that he wants to "see us move forward boldly and quickly."
"I think that we have a strong number of countries on the Security Council who believe this is the right thing to do. But I think these negotiations can be difficult and I am going to push as hard as I can...," he said.
Beijing stressed on Tuesday it wanted any Security Council resolution to promote a diplomatic way out of the nuclear standoff. Iran, which is not attending the conference, is China's third-largest crude oil supplier.
"The well-being of the Iranian people as well as the normal economic, trade, financial and energy exchanges between Iran and many countries in the world -- these legitimate needs and demands should not be undermined," Chinese Vice Foreign Minister Cui Tiankai told reporters on Tuesday.
In another sign of the limits to cooperation on the issue, President Dmitry Medvedev of Russia, another nation with extensive trade with Iran, said any sanctions "certainly must not punish the people" and should focus on nonproliferation.
French President Nicolas Sarkozy, who supports tougher sanctions, said "the moment of truth" was approaching and it was reasonable to expect U.N. action by May at the latest but he also acknowledged any resolution was likely to be weaker than France might like.
Yukiya Amano, head of the U.N. nuclear watchdog, the International Atomic Energy Agency, told Reuters he was concerned Iran might reduce cooperation with U.N. inspectors if further sanctions are imposed on it.
Obama also opened a window on his "frank" talks with Hu regarding U.S. concerns about China's currency, which Washington has long felt is valued too low.
"I think China rightly sees the issue of currency as a ... sovereign issue. I think they are resistant to international pressure when it comes to them making decisions about their currency policy and monetary policy," he said.
The summit's final communique promised greater efforts to block "non-state actors" like al Qaeda from obtaining the building blocks for atomic weapons for "malicious purposes."
While the summit communique included no mechanism to enforce the measures, Obama defended the agreement, saying he believed world leaders were taking their commitments seriously.
Absent from the summit was North Korea, whose nuclear weapons program is a persistent thorn in the side to the West. Summit leaders sent a clear message to Pyongyang by announcing South Korea would host the next nuclear security summit in 2012.
The summit produced several tangible dividends aimed at preventing what Obama said was the world's top security threat -- the risk of terrorists obtaining even a small portion of the estimated 2,000 tons of plutonium and highly enriched uranium that exists in dozens of countries.
Washington and Moscow signed a deal to reduce stocks of excess weapons-grade plutonium. The United States, Canada and Mexico agreed to work together with the International Atomic Energy Agency to convert Mexico's research reactor from the use of highly enriched uranium to low-enriched uranium fuel.
(Additional reporting by Matt Spetalnick, Tabassum Zakaria, Emanuelle Jarry, Andrew Quinn, Paul Eckert, Dan Williams, Patricia Zengerle, Jeff Mason, Ross Colvin, Andreas Rinke, Phil Stewart, Lou Charbonneau, Alister Bull, Arshad Mohammed in Washington; Editing by David Storey and Eric Walsh)