WASHINGTON: President Barack Obama told a global nuclear security summit on Friday that more cooperation was needed to prevent “madmen” from groups like the Islamic State from acquiring a nuke or “dirty bomb”.

Obama told world leaders gathered in Washington that Islamic State's video surveillance of a Belgian nuclear scientist and use of chemical and biological weapons presented a clear statement of intent.

“Because of our coordinated efforts, no terrorist group has succeeded thus far in obtaining a nuclear weapon or a dirty bomb made of radioactive materials,” Obama said.

“There is no doubt that if these madmen ever got their hands on a nuclear bomb or nuclear material, they most certainly would use it to kill as many innocent people as possible,” he added.

The nuclear security summit comes in the wake of attacks in Paris and Brussels that have killed dozens and exposed Europe's inability to thwart destabilising attacks or track Islamic State operatives returning from Iraq and Syria.

The emergence of evidence that individuals linked to those two atrocities videotaped a senior scientist at a Belgian nuclear facility has given the threat added nuclear weight.

“There's roughly 2,000 tonnes of nuclear materials,” around the world Obama said, “and not all of this is properly secured”.

He warned that a bomb containing fissile material the size of an apple could shake the world.

“The smallest amount of plutonium could kill and injure hundreds of thousands of people. It would be a humanitarian, political, economic, and environmental catastrophe with global ramifications for decades,” Obama said.

“It would change our world.”

With Russian President Vladimir Putin boycotting the summit, a major deal on reducing stockpiles is out of reach.

Obama may have to be content with a series of technical measures to improve security, detection and reduce the use of the most dangerous material.