WASHINGTON – President Barack Obama's nuclear summit has paid early dividends: China's agreement to work with the U.S. on possible sanctions against Iran and Ukraine's decision to rid itself of nuclear bomb-making materials.

Obama opened the global security summit Monday night after two days of meetings with selected presidents and prime ministers of the 47 countries assembled to recharge efforts to keep nuclear material out of terrorist hands. It ends Tuesday with a joint declaration to guide future work toward locking away and cleansing the globe of materials still too easily accessible to terrorists.

China's incremental move toward U.S. ambitions to sanction Iran and Ukraine's plans get rid of highly enriched uranium put some wind in Obama's sails as he presses global leaders to join him in locking down all nuclear materials within four years.

Obama's meeting with Chinese President Hu Jintao was the last of the summit warm-up sessions before the U.S. leader sat down with his guests at a working dinner.

After the Hu meeting, White House national security aide Jeff Bader said Iran was a major topic of discussion at the 90-minute session.

They're prepared to work with us," Bader said, interpreting that willingness as "another sign of international unity on this issue.

Obama has been pressing the case that a fourth round of sanctions are needed to persuade Iran to alter its perceived course toward a nuclear weapons capability.

China, while historically averse to tough sanctions and uneasy about potential damage to its trade relationship with Tehran, may indeed be coming on board with Obama. He already has the robust backing of Great Britain, France and Germany. Russia, too, has shown a willingness to join the sanctions effort, which would give Obama the required clean sweep of permanent members of the United Nations Security Council.

But when pressed on whether China had committed to anything specific on the sanctions front, Bader was less direct.

We are going to be — we've started to work that and we're going to be working on that in the coming days — coming days and weeks," he said. Obama wants agreement on sanctions before summer.

In Beijing on Tuesday, Chinese Foreign Ministry spokeswoman Jiang Yu said: "China always believes that dialogue and negotiation are the best way out for the issue. Pressure and sanctions cannot fundamentally solve it.

But she added that China supports a "dual-track strategy," combining diplomacy with the possibility of international sanctions against Iran.

The Ukrainians, who gave a major boost to arms control in 1994 when they agreed to surrender the nuclear weapons they inherited in the collapse of the Soviet Union, agreed to get rid of their weapons-grade fuel by 2012.

Some details are yet to be worked out, including how and where the nuclear fuel will be disposed of, White House press secretary Robert Gibbs said.

The material could be sent to the U.S. or Russia, but Gibbs declined to specify the amount, other than to say it was enough to make several nuclear weapons.

When the summit begins in earnest on Tuesday, the talks will take up Obama's goal of ridding the world of nuclear weapons, with efforts to lock down materials to build those bombs an urgent first step.

Tons of plutonium and highly enriched uranium are believed to be insufficiently protected from international criminal gangs and terrorist organizations.

Al-Qaida is especially notable for its long-standing interest in weapons-usable nuclear material and the requisite expertise that would allow it to develop a yield-producing improvised nuclear device," John Brennan, the White House anti-terrorism chief, told reporters Monday. "And its interest remains strong today.