The UN atomic agency hailed Friday the imminent entry into force of a key nuclear security agreement aimed at preventing extremists wreaking havoc by getting hold of nuclear material.

The announcement by the International Atomic Energy Agency that the accord will come into effect on May 8 follows a summit last week that saw stark warnings about the risks of nuclear terrorism.

"This is an important day for efforts to strengthen nuclear security around the world," IAEA chief Yukiya Amano said.

The accord "will help reduce the risk of a terrorist attack involving nuclear material, which could have catastrophic consequences," Amano said in a statement.

Nicaragua this week ratified the agreement, the arcane-sounding Amendment to the Convention on the Physical Protection of Nuclear Material (CPPNM), the IAEA said.

This takes the number of ratifications to 102, the threshold of two-thirds of states required for the agreement to come into effect in 30 days.

The CPPNM, the only legally binding international undertaking covering the physical protection of nuclear material, entered into force in 1987.

This focused on physical protection of material in international transport.

But the 2005 Amendment widened the scope to cover facilities or material in domestic use, storage and transport.

It makes it legally binding for states to provide adequate protection and foresees enhanced cooperation to recover stolen and smuggled nuclear material, the IAEA said.

Since the mid-1990s, almost 2,800 incidents of illicit trafficking, "unauthorised possession" or loss of nuclear materials have been recorded in an IAEA database.

Only a few involved substances that could be used to make a actual nuclear weapon, but some could be used to create a "dirty bomb" -- a conventional explosive device that disperses radioactive material.

A series of summits in recent years, most recently last week in Washington, have succeeded in reducing the risks of nuclear material falling into the wrong hands, but experts say more needs to be done.

The Islamic State group "has already used chemical weapons, including mustard gas, in Syria and Iraq," US President Barack Obama said on April 1 at the summit.

"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 continue to kill as many innocent people as possible," he said.

Indeed, alarm bells rang in December when Belgian police investigating the November 13 Paris terror attacks found 10 hours of video of the comings and goings of a senior Belgian nuclear official.

One Belgian newspaper reported that the camera, hidden in bushes, was collected by brothers Ibrahim and Khalid El Bakraoui -- two of the suicide bombers in the March 22 Brussels bombings.