
Surrounded by world leaders, President Barack Obama appeared to give the peace sign as they gathered for a 'team photo' during a two-day nuclear summit.

All eyes were on Obama as 54 other presidents and prime ministers joined him in Washington, DC, for crunch talks on Iran and terrorist threats involving nuclear weapons.

There was one set of eyes, however, that was particularly focused on the President - those of Prime Minister David Cameron.

Relations between Cameron and Obama have been strained since the President criticized the Prime Minister for getting 'distracted' during the crisis in Libya and turning it into a 's**t show'.

There was more than metaphorical distance between the pair at today's summit, with Cameron only able to glare at Obama from across the podium as he was elbowed out to the edge of the stage.

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Peace, man: Surrounded by world leaders, President Barack Obama appeared to give the peace sign at the end of a nuclear security summit today

Special relationship in tatters? All eyes were on Obama (left) as 54 other presidents and prime ministers joined him in Washington - including those of David Cameron (right)

Give us a wave, Dave! While the rest of the gathered leaders waved for the cameras, Cameron failed to lift his hand up

New best friend: Cameron was left out again as Obama and Canadian Prime Minister Justin Trudeau chatted during the summit

While Obama fooled around for the cameras, some world leaders - such as Mexican Prime Minister Enrique Peña Nieto (right) - did not look happy

Arms folded: Cameron - fresh from his vacation in Lanzarote - did not appear to be playing ball with an energetic President Obama

Isolated: While Obama and Canadian Prime Minister Justin Trudeau (left) hit it off during the talks, Cameron (right) cut a lonely figure

After a day of tense, sensitive discussions on ISIS and the Middle East, Obama played up for the cameras as he grinned and appeared to flash the peace sign. As it was, he was making clear that there were two individuals waiting to join the line-up.

The President has come under fire for his relaxed attitude in recent weeks.

On a state visit to Argentina, he was seen dancing the tango with an attractive female dancer. On a historic visit to Cuba, he went to a baseball game instead of returning to the United States to respond to the horrific terrorist attacks in Brussels.

Before that, Obama chose not to attend the funeral of former First Lady Nancy Reagan, electing to go to a music festival and eat tacos instead.

While the President was surrounded by power players Chinese President Xi Jinping, Dutch Prime Minister Mark Rutte and Jordanian King Abdullah II ibn Al Hussein at the summit, Cameron was left languishing at the end of a row alongside Algeria's prime minister Abdelmalek Sellal.

Earlier today, Obama spoke of the threat of nuclear weapons falling into the wrong hands, such as those of ISIS terrorists.

The President said no terrorist group had succeeded in getting hold of making a dirty bomb, but said al-Qaeda wanted to and ISIS had already used chemical weapons in the Middle East.

He said there was no doubt that if ISIS 'mad men' got a nuclear bomb, they would use it to kill as many people as possible. Obama gave a chilling warning that such a catastrophic disaster would 'change our world'.

'We have measurably reduced the risk,' Obama said. But he added: 'The threat of nuclear terrorism persists and continues to evolve.'

And he warned that as ISIS comes under greater pressure it will likely carry out more attacks elsewhere.

'As ISIL is squeezed in Syria and Iraq, we can anticipate it lashing out elsewhere, as we've seen most recently and tragically in countries from Turkey to Brussels,' Obama said - using another acronym for ISIS.

Despite Obama's warnings - and his hi-jinks during the photograph with other world leaders - Donald Trump's earlier comments on nuclear weapons cast a shadow over the summit.

The Republican presidential candidate said this week that allowing Saudi Arabia, South Korea and Japan to develop their own nuclear programs would ease strains on U.S. budgets, given the spiraling costs of maintaining America's nuclear umbrella and foreign troop deployments.

'Japan is better if it protects itself against this maniac of North Korea,' Trump said on Tuesday.

'We are better off frankly if South Korea is going to start protecting itself ... they have to protect themselves or they have to pay us.'

Obama was asked about the issue Friday night after Trump said Japan and South Korea should develop nuclear weapons as a deterrent to North Korea.

The president said the United States doesn't want someone in the Oval Office who doesn't recognize the potential trouble in such a development.

'[The statements] tell us that the person who made the statements doesn't know much about foreign policy, nuclear policy, the Korean peninsula or the world generally,' Obama said at the press conference. 'I said before, people pay attention to American elections.'

Obama noted that Trump's comments came up during discussions with leaders at the nuclear summit in Washington.

He said that even countries that are used to a 'carnival atmosphere' in their politics want 'sobriety and clarity' in US elections.

Trump has made several remarks about nuclear weapons lately, even claiming he would not rule out using nuclear bombs in Europe.

Obama's comments come just a day after White House Deputy National Security Adviser Ben Rhodes said that Trump's proposal for Japan and South Korea to have nuclear weapons would be 'catastrophic' for US policy.

'The entire premise of American foreign policy as it relates to nuclear weapons for the last 70 years has been focused on preventing the proliferation of nuclear weapons to additional states,' Rhodes said on Thursday. 'That's been the position of bipartisan administrations, everybody who has occupied the Oval Office.’

Friday's summit in Washington began with Obama hailing the much-criticized nuclear deal with Iran a 'substantial success'.

Planning something? Obama had a cheeky grin on his face as he walked up to the podium before the photograph on Friday

Obama chatted with Dutch Prime Minister Mark Rutte, with most world leaders looking relaxed after the day's nuclear talks

Handsome: Canadian Prime Minister Justin Trudeau maintained his trademark good looks despite a long day of high-level talks

Cool customer: Despite facing criticism for appearing too relaxed in his final year as president, Obama looked chilled as he posed for the photograph while appearing to pull out the peace sign

He said the world has seen 'real progress' as a result of the deal and that Iran was already seeing benefits from the deal.

However, he said it would take some time still before Iran could truly reintegrate with the world economy.

Obama branded the controversial agreement a reminder that when the global community stands together, it can promote common security.

U.S. and Japanese officials also met on Friday to pledge to remove highly enriched uranium from a Japanese research reactor to reduce the risk of theft and nuclear terrorism.

Very few details were released about the agreement or when it will take place.

The two governments also confirmed they have completed removal of materials from another Japanese research reactor that could have been used to make nuclear weapons if they had fallen into the wrong hands. That was part of a separate deal struck in 2014.

More than 700 pounds of plutonium is being shipped from Japan to a U.S. facility in South Carolina, according to Japanese media.

But the state's governor, Nikki Haley, has opposed bringing more plutonium to the site, where tons of it is already stored.

On a busy day for Obama, the President - on the coat tails of an historic trip to Cuba - said Latin America and the Caribbean were now 'free' of highly enriched uranium.

Argentina - another country recently visited by Obama, who was seen doing the tango with an attractive female dancer there last week - aborted a nuclear weapons program in the 1980s and has cooperated with the U.S. on uranium stockpiles.

With the project finally completed, the White House said no country in Latin America or the Caribbean now has more than 1kg (2.2 pounds) of highly enriched uranium.

The United States, in newly declassified statistics, said its own national inventory of highly enriched uranium has dropped from 817 tons two decades ago to 646 tons as of 2013.

On the global front, a strengthened nuclear security agreement was finally poised to take force, extending protections for nuclear materials being used, stored and transported while enacting new criminal penalties for nuclear smuggling. Those tweaks were approved in 2005, but have sat dormant awaiting ratification from a critical mass of nations, reached only in the past few days.

Still, frustration over the slow pace of reducing nuclear stockpiles shadowed the summit, which is Obama's last major push on denuclearization.

The absence of key players - especially Russia - further underscored the lack of unanimity confronting global efforts to deter nuclear attacks.

After six years of prodding by Obama and others before him, the global stockpile of fissile material remains in the thousands of tons. Meanwhile, security officials warn that the radioactive ingredients for a dirty bomb are alarmingly insecure in many parts of the globe.

Ahead of the summit, fewer than half of the countries participating had agreed to secure their sources of radiological material like cesium and cobalt, which are widely present in hospital, industrial and academic settings but could be diverted to make a dirty bomb.

In the wake of terrorist attacks in Brussels and Paris, security officials have raised concerns that the next attack could spread cancer-causing substances across a wide swath of a Western city, wreaking havoc and triggering evacuations.

At the conclusion of a nuclear security summit, where he met with more than 50 leaders to discuss nuclear security, on Friday, Obama gave a press conference.

He told reporters that the United States and Russia are unlikely to further reduce their stockpiles of nuclear weapons during the remainder of his presidency.

Thumbs up: Ukraine's president Petro Poroshenko certainly looked please to have taken his place behind President Barack Obama

... Meanwhile, in the shadows: Cameron was isolated from the power players and looked dejected as he shook hands with UAE foreign affairs minister Abdullah bin Zayed bin Sultan Al Nahyan

Allies: Obama sat next to Japanese Prime Minister Shinzo Abe. Japan and the U.S. struck a deal to remove highly enriched uranium from a Japanese research reactor

He did say, however, that he believes the two countries have put systems in place that will allow for more reductions in the future.

At the close of a nuclear security summit, Obama said that Russian President Vladimir Putin has emphasized 'military might' instead of disarmament, but Obama believes there are still possibilities for progress.

In the meantime, Obama said the world must guard against the proliferation of new, deadlier nuclear weapons.

The president is crediting the United States and Russia with abiding by a bilateral arms reduction treaty.

He said he's tried to strike the right balance between arms reduction and preserving US nuclear weapons capabilities.

As for the world's work to prevent nuclear attacks, Obama said the task is 'by no means finished'.

He said world leaders have made 'significant, meaningful progress' in securing nuclear materials so terrorists can't get them.

But, he said, there is still a large amount of nuclear and radioactive material that must be secured, adding that in some countries, the nuclear arsenal is expanding.

Obama said the dozens of leaders attending the summit agreed to keep strengthening nuclear facilities against cyber-attacks and to bolster defenses against nuclear smuggling.

The work has just begun, Obama said, adding that the vision of preventing the spread of nuclear weapons may not happen in his lifetime.

Also at the press conference, Obama mentioned drones, Turkey and doing business in Iran.

Obama acknowledged that 'civilians have been killed that shouldn't have been' in past US drone strikes, but says the administration is now 'very cautious' about taking strikes where women or children are present.

Asked at the news conference about an increase in the number of people targeted in several drone strikes against extremist targets in Libya, Syria and Somalia, Obama said the 'legal architecture' around the use of drone strikes in the past hasn't been precise.

But in the last several years, he said, the administration has worked hard to prevent civilian deaths.

He added that the United States has to take responsibility when it is not acting appropriately.

The president moved on to Turkey, and said he has been troubled by the country's repression of the press and democratic debate under President Recep Tayyip Erdogan.

Still, he says Turkey is a NATO ally and an important partner in fighting terrorism. Further, Obama said he has a productive partnership with Erdogan.

Obama has, however, spoken openly with Erdogan about trends in Turkey that he calls troubling, particularly in regard to freedom of the press, religion and democracy.

Erdogan was among the 50-some world leaders who joined Obama at a nuclear security summit in Washington.

As for Iran, Obama said the country has to convince international companies that it is safe to do business there as it gains relief from sanctions by complying with the nuclear deal.

Obama he said that the United States and its partners in the nuclear deal need to clarify what business transactions are allowed as the sanctions are lifted.

He added that the Iranians thus far have adhered to the letter of the nuclear agreement.