900 IS fighters held in Syrian Kurdish jails: spokesman
The Kurdish People's Protection Units (YPG) have rounded up thousands of alleged IS members as it battles the group.
"Around 900 IS terrorists are in our jails... from 44 countries," YPG spokesman Nuri Mahmud said.
That is a sharp rise from the figure of 520, given by another Kurdish official last month.
"The war is ongoing and until now we are arresting terrorists," Mahmud explained, referring to ongoing battles against IS in eastern Syria.
"The numbers have increased over the past months from the battles between our forces and IS," he said.
Kurdish authorities have said they will not put any foreign jihadists on trial, and repeatedly called on their home countries to take them back.
But Western countries, reeling from IS-claimed attacks on their own soil, have been reluctant.
"Most countries have been flouting their responsibility," Nuri said.
According to Kurdish foreign affairs official Abdel Karim Omar, Syrian Kurds also hold 550 women and around 1,200 children from the families of IS members.
Alleged fighters are usually detained in jail, while women and children are held separately in camps.
IS seized large swathes of Syria and neighbouring Iraq in 2014, declaring a so-called "caliphate" in areas they controlled.
But multiple offensives in both countries have since decimated that proto-state.
In Syria, the YPG-led Syrian Democratic Forces last month launched a battle to expel the jihadists from their last eastern redoubt of Hajin near the Iraqi border.
Neighbouring Iraq has detained more than 19,000 people accused of connections to the Islamic State group or other terrorism-related offenses, according to a May tally, sentencing to death more than 3,000 of them.
The jailings have raised concerns over potential miscarriages of justices in both Iraq and Syria.