According to Syria’s state news agency SANA, the curfew was announced after fighting broke out in the city, where suspected Daesh detainees were being held.
The clashes occurred a day after the Syrian interim president, Ahmed al-Sharaa, and SDF leader Mazloum Abdi, also known as Mazloum Kobani, agreed to a ceasefire.
Separately, the Syrian army told Al Jazeera on Monday that it had taken full control of al-Shaddadi and the prison holding suspected Daesh detainees, and that troops were searching the city and surrounding areas for escaped fighters.
Syria’s interior ministry said early on Tuesday that 81 of about 120 detainees who had escaped had been recaptured, Reuters reported, adding that efforts were continuing to arrest the remaining fugitives.
The army’s operations authority also told SANA that control of al-Aqtan prison and other security facilities in the city would be transferred to the interior ministry.
Both the Syrian army and the SDF have blamed each other for the prison break.
The army accused the SDF of deliberately releasing the detainees, while the SDF said it lost control of the prison after an army attack, a claim the military has denied.
The SDF said nine of its members were killed and 20 wounded in fighting around al-Aqtan prison.
The group added that the US-led coalition purportedly formed to fight Daesh did not intervene despite repeated calls to a nearby base hosting coalition forces.
Earlier, after the ceasefire agreement signed over the weekend, Damascus said the SDF had agreed to withdraw from areas under its control, including Raqqa and Deir Ez-Zor, two Arab-majority provinces and the location of Syria’s main oilfields.
Hasakah province, where al-Shaddadi is located, remains largely under SDF control.
Daesh was defeated in Iraq in 2017 and in Syria in 2019, but sleeper cells continue to carry out attacks in both countries.