Washington, Apr 2 (IANS): US President Barack Obama said that global efforts to improve nuclear security have removed from circulation material equivalent to 150 nuclear weapons, safeguarding it from extremists.

"That's material that will never fall into the hands of terrorists," Obama said at a news conference on Friday during the closing of the two-day Nuclear Security Summit, here.

The summit, the final of four Obama has held during his presidency since 2010, drew over 50 leaders from around the world to discuss ways to prevent the use of nuclear weapons and better secure nuclear materials, especially from the threat of nuclear terrorism, CNN reported.

"As terrorists and criminal gangs and arms merchants look around for deadly ingredients for a nuclear device, vast regions of the world are now off-limits, and that's a remarkable achievement," Obama said, admitting that much work remains.

Obama cited progress in making large parts of the world free of nuclear materials. South America had already achieved this, and Central Europe and South East Asia were expected to do so later this year.

"Together, we have removed the world's most deadly materials from nuclear facilities around the world," he said.

Despite these gains, Obama said the Indian subcontinent and the Korean peninsula were areas where more could be done to combat proliferation.

Obama said the work done by leaders who gathered from around the globe to discuss nuclear security would help reduce the chances of terrorist groups getting their hands on a nuclear weapon.

"No terrorist group has yet succeeded in getting their hands on a nuclear device. Our work here will help ensure that we're doing everything possible to prevent that," Obama said, adding "This is a threat to us all."

The ongoing challenge, Obama told his counterparts, is to prevent groups like the Islamic State (IS), which have sought nuclear material, from obtaining it or any weapon of mass destruction.

At the opening of the summit on Friday, Obama said the summit's work -- mostly done quietly behind the scenes in the months between high profile gatherings -- served the crucial purpose of reducing the chances that nuclear materials could be stolen.