Syria’s U.S.-backed Kurdish-led force has handed over two Islamic State group militants suspected to be involved in mass killings of Iraqi soldiers in 2014, according to a report by the Syrian Observatory for Human Rights on Friday. The report came a day after the Iraqi National Intelligence Service said it had brought back to the country three IS members from outside Iraq. However, the intelligence service did not provide more details.The group captured around 1,700 Iraqi soldiers after seizing Saddam Hussein’s hometown of Tikrit in 2014. The soldiers were trying to flee from nearby Camp Speicher, a former U.S. base.Shortly after taking Tikrit, IS posted graphic images of IS militants shooting and killing the soldiers. Farhad Shami, a spokesman for the Kurdish-led Syrian Democratic Forces, said the U.S.-backed force handed over two IS members to Iraq. It was not immediately clear where Iraqi authorities brought the third suspect from.The 2014 killings, known as the Speicher massacre, sparked outrage across Iraq and partially fueled the mobilization of Shiite militias in the fight against IS, a Sunni extremist group.Iraq has over the past several years put on trial and later executed dozens of IS members over their involvement in the Speicher massacre.The Observatory said the two IS members were among 20 captured recently in a joint operation with the U.S.-led coalition in the northern Syrian city of Raqqa, once the capital of the Islamic State group’s self-declared caliphate.Despite their defeat in Iraq in 2017 and in March 2019, the extremists sleeper cells are still active and have been carrying out deadly attacks against SDF and Syrian government forces.Shami said a car rigged with explosives and driven by a suicide attacker tried Friday night to storm a military checkpoint for the Deir el-Zour Military Council, an Arab majority faction that is part of the SDF, in the eastern Syrian village of Shuheil. Shami said that when the guards tried to stop the car, the attacker blew himself up killing three U.S.-backed fighters.No one immediately claimed responsibility but the attack but it was similar to previous such explosions carried out by IS militants.The SDF is holding over 10,000 captured IS fighters in around two dozen detention facilities, including 2,000 foreigners whose home countries have refused to repatriate them. The force says fighters of about 60 nationalities had entered Syria years ago and were captured in battle.Kurdish authorities in northeastern Syria have said they will put on trial IS detainees, though it is not clear when such trials would begin.