Fighting has broken out between Syrian government troops and the Kurdish-led Syrian Democratic Forces (SDF), just a day after a ceasefire was announced by the country's state media.
Several SDF fighters were killed and more than a dozen others wounded in Monday's clashes, the group said, as violence erupted around two prisons holding members of the Islamic State group in the northeast of the country.
On Sunday, SDF negotiators agreed a truce in principle with Damascus, but a member of the SDF team, said to include chief commander Mazloum Abdi, told Sky News the talks failed to reach a positive outcome.
The deal, which was signed remotely, appeared to end days of deadly fighting during which government forces captured wide areas of northeast Syria from the SDF.
Further negotiations were due to take place on Monday, but the source said discussions broke down as fighting continued.
Government forces were to blame, having violated the ceasefire, the source said, warning that if attacks persisted, SDF fighters could not disarm and must continue to defend themselves.
The SDF, which was the main US-backed force that fought IS in Syria, controls more than a dozen prisons in the northeast where some 9,000 IS members have been held for years without trial.
Among those detained are extremists thought to have been responsible for atrocities in Syria and Iraq after IS declared a caliphate in June 2014 over large parts of the two countries.
Some of those being held at the Shaddadi Prison in the town of Shaddadeh took advantage of the chaos to escape, the army said in a statement.
The SDF admitted it had lost control of the site, around 31 miles (50km) from the border with Iraq.
Nine of its fighters were killed and 20 others wounded in fighting around another prison, al-Aqtan, northeast of the northern city of Raqqa, the group said.
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A US convoy was seen entering the prison area, apparently to mediate between the two sides, an Associated Press reporter said. Washington has good relations with both sides.
Earlier on Monday, the Syrian government had warned the SDF not to use "cases of terrorism for political blackmail," saying it is ready to implement international law regarding the detainees.
In a statement, Damascus warned the SDF's command not to help IS detainees flee or open up prisons it controls "as a revenge measure or for political pressure".
IS was defeated in Iraq in 2017 and in Syria two years later, but the group's sleeper cells still carry out deadly attacks in both countries.
(c) Sky News 2026: Fighting erupts near prisons holding IS extremists in Syria a day after
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