US President Barack Obama has told the Nuclear Security Summit that a new amendment to a global treaty would halt terrorists like the Islamic State (Isis) getting their hands on weapons of mass destruction. The Convention on the Physical Protection of Nuclear Material has been expanded, tightening protections against nuclear theft and smuggling. So far, 102 countries have ratified the amendment.

The hope is that groups like Daesh (Isis) will now find it even harder to access nuclear material and destructive warheads. IS terrorists have already used chemical weapons in Syria and Iraq, and last week it emerged that jihadists linked to the Paris and Brussels attacks filmed a senior manager at a Belgian nuclear facility.

Obama said the new expanded convention would be effective "soon", but with two major players, Russia and North Korea not represented, the proposal has only a limited effect. Russian President Vladimir Putin snubbed the US-led event in Washington after the two nations recently clashed on Syria and Ukraine.

This is significant as experts believe that the bulk of the worlds "unsecured" nuclear material is stored in Russia or the former Soviet Union states. Kim Jong-Un's North Korea, possibly the most likely to use nuclear weapons after multiple recent tests, is facing further time in the international wilderness and also did not attend.

"Working together, our nations have made it harder for terrorists to get their hands on nuclear material," he told the Nuclear Security Summit in Washington DC. More than 50 world leaders have attended the summit in Washington over the past two days.

Obama is concerned that terrorists may gain material needed for a so-called "dirty bomb", as he embarks on attempting to reduce the global stockpile of atomic weapons in his last 10 months in office. He added that roughly 2,000 tons of nuclear material is currently stored across the globe and "not all of this is properly secured."

"ISIL has already used chemical weapons - there is no doubt if these madmen ever got their hands on a bomb or nuclear material they would use it to kill as many as possible," Obama added, saying that a bomb containing nuclear material the size of an apple could be catastrophic.

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