The Security Council has been looking at what one senior UN official has described as a "very complex and evolving issue": foreigners travelling to conflict zones to join terrorist groups fighting there.
Dianne Penn reports on the briefing delivered on Tuesday by the head of the UN Office of Counter-Terrorism, Vladimir Ivanovich Voronkov.
Mr Voronkov began his briefing by laying out the scale of the problem.
He said it's estimated that at one time, more than 40,000 combatants from over 110 countries had joined terrorist groups fighting in Syria and Iraq.
However, flows to the region have "significantly decreased", he said, thanks to travel measures implemented by countries and military victories against the extremist group ISIL, also known as Daesh.
Still, combatants have since tried to relocate to Libya, Yemen and Afghanistan, fuelling existing conflicts in these countries.
At the same time, some 5,600 fighters from 33 nations have returned home, many of whom are equipped to carry out attacks on their native soil, or eager to drum up new recruits to their cause.
"Returning foreign terrorist fighters pose an enormous challenge with no easy solution. A tempting response, and certainly the easiest one, would to be throw all returnees into prison or even to do what would stop them coming home at all. But full compliance with international law is vital to combat the threat of foreign terrorist fighters."
Mr Voronkov reported that countries are increasingly strengthening legal frameworks and their criminal justice systems to prevent and respond to the threat posed by foreign terrorist fighters.
He looked ahead to June 2018 when the first-ever UN summit of heads of counter-terrorism agencies will take place.
Source: United Nations Radio