UNITED NATIONS: More than 25,000 foreign fighters from some 100 countries are linked to al Qaeda and Islamic State, with Syria and Iraq comprising a "veritable international finishing school for extremists," United Nations experts reported to the U.N. Security Council.

The experts, who monitor al Qaeda sanctions violations, said in a report seen by Reuters that along with some 22,000 foreign fighters in Syria and Iraq, there were also 6,500 in Afghanistan and hundreds more in Yemen, Libya, Pakistan and Somalia.

At a meeting of the 15-member Security Council chaired by U.S. President Barack Obama in September, the experts were asked to report within six months on the threat from foreign fighters joining Islamic State, which has declared a caliphate in Syria and Iraq, Nusra Front in Syria and other al Qaeda-linked groups.

"For the thousands of (foreign fighters) who traveled to the Syrian Arab Republic and Iraq ... they live and work in a veritable 'international finishing school' for extremists as it was in the case in Afghanistan during the 1990s," the experts wrote in their report submitted to the council late this month.

Al Qaeda founder Osama bin Laden found refuge in Afghanistan in the 1990s, where the militant group - blamed for the Sept. 11, 2001 hijacked airliner attacks on the United States - ran training camps.

The U.N. experts said Libya had increasingly becoming a training base for foreign fighters bound for the Middle East, but since the start of 2015 there had been a reverse flow of fighters from the Middle East to Libya.

"Those who eat together and bond together can bomb together," the experts wrote. "The globalization of al Qaeda and associates, particularly visible with (Islamic State), but also evident with al Qaeda in the Arabian Peninsula (in Yemen), creates a deepening array of transnational social networks."

The report warned of a medium-term threat from the new generation of foreign fighters through "plug and play social networks for future attack planning - linking diverse foreign fighters from different communities across the globe."

It also said an unintended consequence of defeating Islamic State in Syria and Iraq could be the scattering of violent foreign fighters across the world.

The Security Council adopted a resolution in September demanding all states make it a serious criminal offense for their citizens to travel abroad to fight with militants, or to recruit and fund others to do so.