The leaders of more than 50 nations who met in Washington about nuclear security and terrorism agreed on the actions they will take together to reduce the risks facing the world, but President Barack Obama says the hard work starts now, building on the summit’s accomplishments.

The global effort to keep nuclear materials secure has made important progress, Obama told Americans Saturday. “As terrorists and criminal gangs look around for the deadly ingredients for a nuclear device, vast regions of the world are now off limits.”

Summarising the summit, Obama said “no terrorist group has yet succeeded in obtaining a nuclear device or producing a dirty bomb using radioactive materials.” However, he added that al-Qaida, Islamic State and other terror groups certainly have tried to do so.

U.N. Secretary-General Ban Ki-moon, who was at the summit, “wholeheartedly” endorsed the communique and action plan agreed by the participants. He called on the entire world to sustain and build on the momentum the summit achieved, by “developing concrete recommendations on the nexus between nuclear terrorism and cyber security.”

Obama is following up the meetings on nuclear security with White House talks on Monday with NATO’s secretary-general, Jens Stoltenberg. They will discuss the fight against Islamic State extremists and other terrorists, as well as the refugee crisis in Europe and plans for a NATO summit conference in Poland three months from now.

•Excerpted from a VOA report. Photo shows President Obama.