At the fourth and final Nuclear Security Summit (NSS) in Washington, DC, world leaders have assembled to confront a diverse array of nuclear threats.

Those in attendance included French President Francois Hollande, Dutch Prime Minister Mark Rutte, Japanese Prime Minister Shinzo Abe and UK Prime Minister David Cameron. Russian President Vladimir Putin boycotted the meeting, which, at a time when tensions between Washington and Moscow are increasing, will add to the doubting success of the summit.

Nuclear Security Summit
US President Barack Obama speaks during his trilateral meeting with South Korean President Park Geun-Hye and Japanese Prime Minister Shinzo Abe at the Nuclear Security Summit in WashingtonKevin Lamarque/Reuters

President Barack Obama aimed to persuade dozens of countries to rid themselves of bomb-making materials or reduce and safeguard stockpiles. Yet with less than 10 months left in office, it has left him with limited time to follow through on one of his signature foreign policies. Fears have risen in light of the recent Brussels attacks, fuelling concerns that the Islamic State could eventually develop and activate 'dirty bombs' – a topic which may well be high priority during the summit.

In conjunction with the Nuclear Security Summit, IBTimes UK takes a look at the nine countries who have already have nuclear weapons.

US
According to the Federation of American Scientists, the US has an estimated inventory of 7,200 nuclear warheads, 1,900 of which are strategically deployed.

US military drill
An F/A-18 Hornet prepares to take off from the nuclear-powered aircraft carrier USS John C Stennis, during a joint military drill between South Korea and the USReuters

Russia

It is estimated that Russia have around 7,500 nuclear warheads, although the total is uncertain because there is no accurate count of tactical weapons. Of these, an estimated 1,750 are strategically deployed.

Russia military parade
Russian servicemen, dressed in historical uniforms, line up as they take part in a military parade rehearsal in Red Square near the Kremlin in central Moscow, RussiaMaxim Shemetov/Reuters

France
France has cut down its amount of arsenal to approximately 300 nuclear warheads.

France
France's national colours trail over the Arc de Triomphe and the Champs Elysees avenue during the annual Bastille Day parade in ParisBenoit Tessier/Reuters

UK
Britain's nuclear stockpile consists of about 200 strategic and 'sub-strategic' warheads on four Vanguard-class nuclear-powered ballistic missile submarines.

UK
Welsh Guards parade during annual Trooping the Colour ceremony at Horse Guards Parade in central London in BritainReuters

China
China is estimated to have around 250 strategic and tactical nuclear weapons, and stocks of fissile material sufficient to produce a much larger arsenal.

China
Chinese People's Liberation Army Navy recruits chant slogan during a parade to mark the end of a semester at a military base of the North Sea Fleet, in Qingdao, Shandong ProvinceReuters

India
In May 1998, India formally declared itself a nuclear weapon state. New Delhi is likely to have manufactured weapons-grade plutonium for at least 100 warheads.

India
A surface-to-surface Agni V missile is launched from the Wheeler Island off the eastern Indian state of OdishaReuters

North Korea
North Korea tested its fourth nuclear bomb in January 2016.

north korea
Soldiers march past the podium during a military parade to celebrate the centenary of the birth of DPRK's founder Kim Il-sung in PyongyangReuters

Pakistan
Pakistan is believed to possess a nuclear inventory of 100 or so warheads.

pakistan
Pakistan's Chief of Army Staff General Ashfaq Parvez Kayani (C) with senior army officials and scientists of Pakistan Army?s Strategic Force CommandReuters

Israel
It is understood that Isreal holds a sizeable amount of nuclear arsenal. However, the country maintains a policy of nuclear ambiguity. Based on estimates of the plutonium production capacity of the Dimona reactor, Israel has enough plutonium for approximately 100-200 advanced nuclear explosive devices.

israel
An Israeli soldier ties a national flag to the antenna of a tank as his unit prepares to enter the northern Gaza StripReuters