Washington: Terrorist organisations like al Qaeda and ISIS will use nuclear weapons if they ever get hold of it, US President Barack Obama warned on Saturday a day after he hosted leaders from over 50 countries including India for the Nuclear Security Summit (NSS).

"Fortunately, because of our efforts so far, no terrorist group has yet succeeded in obtaining a nuclear device or producing a dirty bomb using radioactive materials," Obama said in his weekly web and radio address to the nation.

"We know that al Qaeda has tried. ISIL has already used chemical weapons in Syria and Iraq. And, if they ever got hold of a nuclear weapon or nuclear material, we have no doubt they'd use it," the US President said.

"That's why we've been leading a global effort to secure the world's nuclear materials. With summits like this, we've made important progress. Working with other nations, we have removed or secured enough nuclear material for more than 150 nuclear weapons material that will now never fall into the hands of terrorists," he said.

Obama said whole of South America is now free of these deadly materials and Central Europe and Southeast Asia are on track to be free of them later this year.

That means that as terrorists and criminal gangs look around for the deadly ingredients for a nuclear device, vast regions of the world are now off limits.

"This is a remarkable achievement. And at this summit, we pledged to keep up our efforts to prevent the world's most deadly networks from obtaining the world's most deadly weapons," Obama said.

According to the US President, the NSS was another opportunity to make sure the world remains united and focused on destroying ISIL.

"A majority of the nations who came here are part of our global coalition against ISIL. A number of our countries have been targeted by ISIL. Just about all our nations have seen citizens travel to join ISIL in Syria and Iraq," he said.

Noting that ISIL continues to lose ground in Syria and Iraq, Obama said the US-led coalition continues to take out its leaders, including those planning terrorist attacks against countries.

"They're losing their oil infrastructure and revenues. Their morale is suffering," he said.