The Islamic State group on Tuesday released 270 of an estimated 400 civilians, most of them women and children, who had been kidnapped on Saturday when the terror insurgency's fighters attacked Syrian government-held areas around the eastern provincial capital of Deir al-Zor.
The Syrian Observatory for Human Rights, a monitoring group, drew attention to the abduction on Sunday, saying that families of pro-government fighters were among those abducted.
"There is genuine fear for their lives, there is a fear that the group might execute them as it has done before in other areas," said SOHR director Rami Abdulrahamn. Syria's state news agency SANA said earlier that at least 300 people, including women and children, had been killed during the attacks in Deir al-Zor, but it made no mention of people getting kidnapped.
In announcing the partial release on Tuesday, SOHR also noted that the ultra-hardline group rounded up another 50 men on Tuesday during raids on houses in areas seized during four days of fighting in the city. Abdulrahman said that IS has kept male prisoners between the ages of 14 and 55 for more questioning.
"Those who they see have ties with the regime will be punished and those who (do) not must undertake a religious course based on the group's interpretation of Islam," he said.
The civilians released will remain in Islamic State-run villages in the province of Deir al-Zor, which links the group's de facto capital in Raqqa with territory controlled by the militant group in neighboring Iraq.
IS, which controls of most of the province, has laid siege since last March to remaining government-held areas in the city of Deir al-Zor.
Residents are facing severe food shortages and sharply deteriorating conditions. Of those under siege in the city, 70 percent are women and children, and many have been displaced from their homes elsewhere and are living in temporary shelters.
A source close to the Syrian government told Reuters on Saturday that some of those killed had been beheaded. Those reports could not be independently verified.
IS has previously carried out mass killings following military assaults in Iraq and Syria, including the slaughter of 200 soldiers captured from the Tabqa airbase in Raqqa province, and hundreds of members of the al-Sheitat tribe in Deir al-Zor in 2014.