US President Barack Obama was on Tuesday to urge world leaders to lock down nuclear material and arms to ensure extremists can never hold nations hostage with the threat of an atomic attack.
Obama was to huddle with the leaders of 46 other nations behind closed doors for the second day of a nuclear security summit with the aim of securing loose materials in military and civilian stockpiles worldwide within four years.
"I think at the end of this we're going to see some very specific, concrete actions that each nation is taking that will make the world a little bit safer," Obama said Monday.
The two-day gathering, the biggest hosted by a US leader since 1945, saw Obama meet Monday with Chinese President Hu Jintao and others in consultations he described as "impressive."
In an early boost to the unprecedented talks, Obama won pledges from Ukraine, Chile and Canada to either renounce or reduce their stockpiles of enriched uranium which can be used to make a bomb.
The ex-Soviet republic of Ukraine, site of the 1986 Chernobyl nuclear power plant explosion, said Monday it would give up 90 kilos (180 pounds) of highly enriched uranium, equating to several bombs.
But the conference threatened to be overshadowed by growing tension on Iran, which the United States and its allies accuse of covertly working on a nuclear weapon. Iran says it is pursuing only civilian power.
Obama met Monday with Chinese President Hu Jintao seeking to persuade him to join the growing drive to impose a fourth set of sanctions on Iran for its refusal to rein in its suspect enrichment program.
China, a veto-wielding member of the Security Council, reaffirmed its longheld position and said Tuesday sanctions were not the answer to the Iranian atomic standoff.
"China always believes that dialogue and negotiation are the best way out for the issue. Pressure and sanctions cannot fundamentally solve it," foreign ministry spokeswoman Jiang Yu told reporters.
But a top White House official said Obama and Hu had agreed their delegations would work together at the United Nations.
"They are prepared to work with us," said Jeff Bader, Obama's top official responsible for East Asia on the National Security Council.
"The two presidents agreed the two delegations should work together on sanctions."
Iran, which has dismissed the Washington summit, defiantly said it was organizing its own nuclear conference to be held in Tehran on Saturday and Sunday with foreign ministers from 15 countries.
The conference was being held following a "collective will of some independent and free-willed nations to genuinely confront the use of nuclear weapons in today's world," Iranian foreign ministry spokesman Ramin Mehmanparast said, without naming the countries.
French President Nicolas Sarkozy, who is in Washington, said meanwhile that his country could never give up its nuclear weapons "on a unilateral basis, in a world as dangerous as the one in which we live today."
"I cannot jeopardize the security and safety of my country," Sarkozy told CBS News late Monday.
He also hinted that countries like the United States and Russia should take the lead in whittling down their own huge nuclear stockpiles, rather than expecting France, which has fewer atomic weapons, to disarm.
Pakistan's Prime Minister Yousuf Raza Gilani, who controls the Islamic world's only declared nuclear arsenal, also rebuffed calls to halt production of fissile material.
Instead, Gilani made a new pitch to the United States -- which relies on Pakistan in its campaign against Islamic extremists -- to support the blackout-plagued nation in developing civilian nuclear power.
"I assure you that Pakistan, as a responsible nuclear state and an emerging democracy, stands with the international community in its effort to make this world a better place to live in," Gilani told reporters.
The United States and Russia were meanwhile Tuesday to sign an accord on eliminating plutonium reserves, enough "for several thousand nuclear weapons," according to the State Department.
The goal of the summit is to make sure that worldwide stocks of separated plutonium and enriched uranium are destroyed or accounted for and therefore unable to fall into the hands of militant groups.