Leaders of 47 countries assembled to recharge efforts to keep nuclear material out of terrorist hands as President Barack Obama’s summit began in earnest on Tuesday.

It ends on Tuesday evening with a joint declaration to guide future work toward locking away and cleansing the globe of materials still too easily accessible to terrorists.

In an opening address to assembled leaders, Mr. Obama noted that the risks of nations going to war with nuclear weapons had decreased while “the risk of a nuclear attack has gone up,” -- a reference to the threat of terrorists getting their hands on nuclear materials.

Mr. Obama’s remarks were advance excerpts of his speech released Tuesday by the White House.

China’s agreement to work with the U.S. on possible sanctions against Iran and Ukraine’s decision to get rid of highly enriched uranium put some wind in Mr. Obama’s sails as he presses global leaders to join him in locking down all nuclear materials within four years.

Mr. 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 Monday night.

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,” Mr. Bader said, interpreting that willingness as “another sign of international unity on this issue.”

The upbeat assessment reflected a recent warming of U.S.-Chinese diplomatic ties. Still, the meeting produced no breakthroughs. And Chinese spokesman Ma Zhaoxu did not mention sanctions in a statement on Mr. Hu’s meeting with Mr. Obama.

Mr. Ma said China hopes all parties will step up diplomatic efforts and seek ways to resolve the Iranian nuclear issue through negotiations.

“China and the United States share the same overall goal on the Iranian nuclear issue,” the Chinese statement said.

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.

In Tehran on Tuesday, Iran expressed doubts that China would back the U.S. push for new sanctions. Foreign Ministry spokesman Ramin Mehmanparast said he did not think Hu was signaling that with his comments.

Tehran doesn’t “consider the statement as approval of the U.S. stance and unfair actions,” he told reporters. “Our interpretation is different.”

The U.S. already has the robust backing of Great Britain, France and Germany in adopting further sanctions against Iran. Russia, too, has shown a willingness to join the sanctions effort, meaning the required clean sweep of permanent members the United Nations Security Council.

Brazil and Turkey, which both hold non-permanent seats on the U.N. Security Council, are studying an alternative proposal to deal with Iran’s controversial nuclear program, Brazilian Foreign Minister Celso Amorim said Monday.

Brazilian President Luiz Inacio Lula da Silva and Turkish Prime Minister Recep Tayyip Erdogan talked about designing a strategy different from sanctions at a meeting Monday, Amorim said.

Amorim told a news conference that Brazil agrees with the permanent members of the Security Council seeking a “diplomatic solution,” but has a different perspective on how the issue should be approached.

Erdogan said at a speech on the sidelines of the conference Monday that his country does not want Iran or any other nation to have nuclear weapons.

While the United States worries about Iran’s nuclear program, Turkey has its own concerns about Israel’s nuclear program. Israeli Prime Minister Benjamin Netanyahu opted not to attend Obama’s summit, and insiders said he had expected Turkey and Egypt to use the conference as a platform to challenge him over his country’s widely assumed nuclear arsenal, which the Jewish state never has acknowledged.

Iran’s U.N. Ambassador Mohammad Khazee on Monday declared Obama’s new nuclear policy, which excludes Iran from a U.S. pledge not to use nuclear weapons against countries that do not have them, an act of “state terrorism” because it threatens nations with weapons of mass destruction.

Meanwhile, 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 he declined to specify the amount, other than to say it was enough to make several nuclear weapons.

The focus of the summit is tons of plutonium and highly enriched uranium are believed to be insufficiently protected from international criminal gangs and terrorist organizations.

A new report from a Harvard non-proliferation expert, for example, finds that Pakistan’s small but growing stockpile faces “immense” threats and is the world’s least secure from theft or attack.

However, Pakistani Prime Minister Yusuf Raza Gilani said his country’s nuclear weapons are well-guarded.

The officials at the summit are expected to sign a joint declaration to guide future work toward locking away and cleansing the globe of materials still too easily accessible to terrorists.

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