BAGHDAD — As Iraqi forces raided the last Islamic State strongholds in Mosul's Old City, security forces arrested dozens of foreign fighters, including Russian, German and Chechen women who had joined the militant group.

Many other IS foreign fighters have returned to their home countries. The European Union's counterterrorism coordinator, Gilles de Kerchove, said Aug. 9 that an estimated 5,000 European fighters, mostly from France and Belgium, had been trained in Syria and Iraq, and that one-third of them had returned home. France's interior minister said Aug. 6 that 271 French jihadi militants had returned from war zones in Iraq and Syria.

But not all of the fighters could make it back to their home countries, as some militants were captured by Iraqi forces. Reuters published videos July 13 showing a group of shirtless IS fighters sitting on rubble in Mosul. The Iraqi parliamentary Security and Defense Committee last month estimated the total number of foreign fighters who entered Iraq and joined IS ranks to be 30,000, of which 28,000 were killed. However, other studies show far lower numbers.

Hakim Zamili, a member of the committee, said that of those 30,000 fighters, 9,000 came from East Asia, 8,000 from Europe, 6,000 from Tunisia and 3,000 from Saudi Arabia. “Those who managed to flee from Iraq returned to their homelands,” Zamili said.