More than 10,000 Islamic State fighters are estimated to remain active in Iraq and Syria two years after the militant group’s defeat, and their attacks have significantly increased this year, the U.N. counter-terrorism chief said Monday.

Vladimir Voronkov told the U.N. Security Council that Islamic State fighters move freely “in small cells between the two countries.”

He said the Islamic State extremist group — also known as IS, ISIL and ISIS — has regrouped and its activity has increased not only in conflict zones like Iraq and Syria but also in some regional affiliates.

“However, in non-conflict zones, the threat appears to have decreased in the short term,” he said. “Measures to minimize the spread of COVID-19, such as lockdowns and restrictions on movement, seem to have reduced the risk of terrorist attacks in many countries.”

Nonetheless, Voronkov said, “there is a continued trend of attacks by individuals inspired online and acting alone or in small groups, which could be fueled by ISIL’s opportunistic propaganda efforts during the COVID-19 crisis.”

He said the COVID-19 crisis has highlighted the challenges of eliminating the threat of terrorism, pointing to actions by IS and other terrorist groups seeking “to exploit the far-reaching disruption and negative socioeconomic and political impacts of the pandemic.”

But Voronkov said the pandemic’s impact on IS recruitment and fundraising activities remains unclear, and there is no clear indication of a change in the extremist group’s strategic direction under its leader, Abu Ibrahim al-Hashimi al-Quraishi.

Turning to Africa, Voronkov said the Islamic State in West Africa Province “remains a major focus of ISIL global propaganda, and its total membership of approximately 3,500 makes it one of the largest of the remote `provinces.’” He said it continues to reinforce links with the Islamic State in the Greater Sahara, “which remains the most dangerous group in the tri-border area of Burkina Faso, Mali, and the Niger.”

While IS only has “a few hundred fighters in Libya,” he said, they have been exploiting ethnic tensions and represent “a potent threat capable of broader regional impact.” He also pointed to worrying attacks by the Islamic State Central Africa Province in Congo and Mozambique, “including complex attacks and brief takeovers of villages.”

In Europe, Voronkov said, the main threat comes from “Internet-driven, homegrown terrorist radicalization,” citing three ISIL-inspired attacks in France and two in the United Kingdom. He also noted “acute concerns ... about radicalization and failed rehabilitation in prisons, and the imminent release of dangerous inmates with a terrorism background or connections.”

In Afghanistan, Voronkov said, ISIL’s affiliate has conducted high-profile attacks in various parts of the country, including Kabul, and seeks to use Afghan territory “to spread its influence across the region” and to attract fighters who oppose the recent peace agreement between the U.S. and the Taliban.

Elsewhere in Asia, ISIL claimed its first attack in the Maldives in April, he said, and attacks on security forces in southeast Asia occur regularly though government counter-terrorism operations have kept up pressure on the extremists.

Voronkov said the COVID-19 crisis has further complicated “the already dire and unsustainable situation” of thousands of people with suspected links to IS who are stranded in camps in Syria and Iraq, especially women and children.

“Repatriation, prosecution, rehabilitation, and reintegration and the protection of the vulnerable have become ever more urgent,” he said.

While some countries have repatriated their nationals, especially children, many have not.

Voronkov reiterated U.N. Secretary-General Antonio Guterres’ call for all countries to implement international law and bring home all their stranded women, men and children.

“The global threat from ISIL is likely to increase if the international community fails to meet this challenge,” the head of the U.N. Office of Counter-Terrorism warned.

U.S. Ambassador Kelly Craft said the United States shares the secretary-general’s concern and has brought back American citizens and prosecuted them where appropriate.

Despite the Islamic State's defeat on the battlefield, she said, “we must work together to ensure that the population of detained foreign terrorist fighters as well as their family members displaced in Syria and Iraq do not become the nucleus of an ISIS 2.0.”

Russia’s U.N. Ambassador Vassily Nebenzia, whose country is Syria’s main ally, said the global terrorist threat from ISIL remains high, and its leadership is planning terrorist attacks in the border area between Syria and Iraq.

“At the same time, the terrorists do not intend to give up plans to revive the `caliphate' in Iraq,” he said. “ISIL continues to build up its combat potential and is seeking to expand the area and scope of terrorist attacks in the country.”

Nebenzia said ISIL’s organization and tactics suggest “that it has now fully transformed into a network structure with a high degree of autonomy of branches and `sleeping cells’ in various countries and regions of the world.”