Russian President Vladimir Putin said Thursday that Daesh militants have detained nearly 700 hostages in parts of Syria that are controlled by U.S.-backed forces and issued an ultimatum saying they would execute 10 people every day.

Speaking in the Black Sea resort city of Sochi, Putin said the hostages included several U.S. and European nationals, adding that Daesh was expanding its control in territory controlled by U.S. and U.S.-backed Syrian Democratic Forces (SDF) forces.

Putin did not specify what the militants' demands were.

"They have issued ultimatums, specific demands and warned that if these ultimatums are not met they will execute 10 people every day. The day before yesterday they executed 10 people," Putin told the Valdai discussion forum in Sochi.

The TASS news agency reported on Wednesday that Daesh terrorists had taken around 700 hostages in Syria's Deir el-Zour province after attacking a refugee camp in an area controlled by U.S.-backed SDF forces on Oct.13.

TASS said the terrorists had kidnapped around 130 families and taken them to the city of Hajin.

The U.S. has partnered with the SDF, predominantly led by the PKK-affiliated People's Protection Units (YPG), in their fight against Daesh terror group, despite warnings from Turkey against the repercussions of using one terrorist group to defeat another.