One of the biggest security threats for rational states has been the use of nuclear bombs by rogue non-state actors who do not abide by international law on the use of nuclear weapons.
As the threat from the ISIS continues to escalate, there is obvious concern over the possibility it could get its hands on nuclear weapons. While some analysts argue that it may not be able to acquire nuclear bombs, Matthew Bunn, a nuclear security expert from Harvard, feels that it is very possible. The Nuclear Security Summit in 2016 also highlighted the threat. 
Options for ISIS: State actors and non-state entities
In May 2015, reports quoted ISIS members that they were “infinitely” close to availing themselves of nuclear weapons. It is not the first time the threat of nuclear and radiological terrorism has emanated from a non-state actor. In 2010 and 20111, Al Qaeda was also reported to be attempting to acquire them. Given the billions of dollars that ISIS has, financially it is certainly possible.
What makes the threat loom larger is that ISIS’ influence is no longer confined to Syria and Iraq, and its region of influence is expanding day by day. In May 2015, there were also reports that ISIS could acquire nuclear weapons from Pakistan.  However, at this point in time when there is extreme pressure mounting on states to join hands with the US in the war against ISIS, Pakistan may not want to risk proliferating its nuclear weapons to non-state actors.
After the Brussels attack in 2016, there were reports that ISIS was seeking radioactive materials from the nation’s Doel nuclear power plant to make some sort of dirty bomb. The standard purpose of nuclear bombs is as a weapon of deterrence, but for ISIS they are a weapon of attack and terrorism. Therefore, a basic dirty bomb developed from radioactive material is not impossible. It is however, unlikely that ISIS would build bombs from highly enriched uranium (HEU) or from plutonium. But dirty bombs serve their purpose, and reports in 2015 said smugglers tried to sell cesium, a component used to make dirty bombs, to ISIS. It was also reported that these groups also tried to smuggle uranium isotopes, which is alarming.  These groups also declared in 2011 that they had access to plutonium and could provide samples to ISIS for free to make dirty bombs. 
In 2013, reports surfaced that Saudi Arabia could avail itself of nuclear weapons from Pakistan, should it feel the need to do so, given its historic connection with Pakistan’s nuclear weapons program – which it funded.  Nuclear weapons in Saudi territory could also fall into the hands of ISIS, and there is a clear fear that so could nuclear bombs stored in the Incirlik Air Base near Turkey’s border. 
Threat and solutions
There is no doubt that ISIS is keen to attack the United States on its home territory.  Dirty bombs would suit this purpose, and would have a great impact, both in terms of destruction and propaganda. Unlike state actors against whom the Americans can strengthen their deterrence, ISIS has no fixed areas of operations and therefore the threat of massive retaliation or mutually assured destruction would not deter adversaries.
As Joe Cirincione, President of the Ploughshares Fund, puts it, the more military success is achieved against ISIS, the more it would demand such weapons.  He recommends the US should stop spending billions of dollars on its nuclear arsenal and divert funds to form mechanisms that would prevent radioactive materials falling into the hands of non-state actors. 
The Associated Press has reported that Eastern European gangs are exploiting the strained relations between Russia and the United States to sell radioactive materials to ISIS.  Moscow and Washington, DC, must not let this happen, and, at the very least, cooperate in matters pertaining to nuclear arms control and non-proliferation. The recent Russian withdrawal from the Plutonium Disposal Management Agreement (PDMA) in 2016, however, does not show US-Russia nuclear arms control efforts in a positive light.
Tough road ahead
At the 2016 Nuclear Security Summit, US President Barack Obama gave assurances that nuclear materials would not fall into the hands of terrorist organizations, and he further stated that “vast regions of the world are now off-limits” that previously could have enabled terrorist organizations to develop nuclear bombs.  But given the widespread influence of ISIS, the task of preventing nuclear bombs or radioactive materials from falling into its hands will not be easy.
Debalina Ghoshal is a Research Fellow at the Centre for Human Security Studies, Hyderabad.