President Barack Obama's nuclear security summit took a step toward lowering the risk of a terrorist group getting an atomic weapon, but real progress depends on countries keeping the promises they made.
At the two-day Washington summit the United States and 46 other countries agreed on a voluntary "action plan" to secure all vulnerable nuclear material over the next four years.
But the final communique glossed over disagreements on divisive issues like whether to continue making weapons-grade uranium and plutonium and came up with no binding commitments.
Mr Obama called it "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."
Analysts said it was significant that the world's oldest nuclear powers the United States, France, Britain, Russia and China sat at a table with India and Pakistan, both nuclear-armed nations, and Israel, which is presumed to have nuclear weapons but neither confirms nor denies it.
The three are outside the 1970 nuclear Non-Proliferation Treaty aimed at stopping the spread of atomic weapons.
Kenneth Luongo, head of US-based Partnership for Global Security said it was important that developed and developing powers had come together and agreed "there's a problem with nuclear security and are prepared to deal with it."
He said the communique and action plan were vague and weakened by qualifying phrases and noted its implementation was voluntary.
"But the fact that this discussion is happening at the highest levels for the first time is very significant and should not be discounted," Mr Luongo said.
Now the real work on improving nuclear security could begin. "Once the lights go down tonight, leaders need to hit the ground running on implementation," Mr Luongo said.
US officials say there are about 2,000 tons of weapons-grade uranium and plutonium worldwide, but nuclear non-proliferation experts say that there is almost certainly more that has never been declared.
Analysts say that terrorists could theoretically build a crude but deadly nuclear device - or possibly something more sophisticated - if they have the money, technical personnel and required amount of fissile material. They say groups like al-Qaeda have been trying to get atom bomb ingredients.
Obtaining arms-grade material is the biggest challenge, which is why keeping it secure is so important.
An improvement in nuclear security also has implications for the civilian nuclear power industry, which has seen a rebirth in recent years partly because it produces few greenhouse gas emissions harmful to the climate.
David Albright, a former UN arms inspector and head of the Institute for Science and International Security think-tank, noted disagreements over civilian use of plutonium.
"Obama's willing to set aside his objections (regarding plutonium use) to keep France involved," he said. France is one of the world's top producers of MOX nuclear fuel, which is made from recycled plutonium.
Environmental activists and other critics of MOX say the transport of nuclear waste and reprocessed plutonium leaves the materials vulnerable to accidents or theft.
Albright said that France - which gets 80 per cent of its electricity from nuclear power, the highest in the world - had been concerned Mr Obama might use the summit to highlight the dangers of nuclear energy and play down its positive side.
But Mr Obama did not do that and France realised that the summit could prove helpful to the nuclear industry, he said.
Ultimately, Mr Albright said, the success or failure of the summit will depend on whether individual countries live up to the commitments they made.
Success will also depend on continued US leadership.
Securing nuclear material would be a good start but not sufficient, analysts say. UN secretary-general Ban Ki-moon urged the world to ban the production of atom bomb material.
The 65-country UN-backed Conference on Disarmament in Geneva has long been considering such a ban. But Pakistan has blocked the start of negotiations, arguing that it would put it at a permanent disadvantage to India, with which it has fought three wars since independence in 1947.
Iran's nuclear standoff with the West cast a shadow over the summit.
A day after discussing Iran with Chinese president Hu Jintao, Mr Obama expressed gratitude that China had agreed to help negotiate a new UN sanctions resolution on Iran but said Beijing still has concerns about the issue.
He said he had argued in talks with Mr Hu on Monday that there must be consequences for Iran's violations of its international obligations.
"The Chinese are obviously concerned about what ramifications this might have on the economy generally," Mr Obama said. "Iran is an oil-producing state."
Mr Obama last month said he hoped to get a new sanctions resolution ready within weeks. He declined to provide a timetable yesterday but said he did not want a long, drawn-out process that takes months.
"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.
Mr Obama also opened a window on his talks with Mr Hu regarding US 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.