File Photo: Kurdish forces deploy in Syria s northern city of Hasakeh amid ongoing fighting with the Islamic State group. AFP
"Sixteen local fighters and three members of the Syrian Democratic Forces (SDF) have been killed" during the clashes in several villages in the east of Deir Ezzor province, the Syrian Observatory for Human Rights said, raising an earlier toll.
Three civilians including two children have also been killed in the violence, it added.
The US-backed, Kurdish-led SDF spearheaded the battle that dislodged Islamic State group fighters from the last scraps of territory they controlled in Syria in 2019.
The affiliated group, the Deir Ezzor Military Council, is led by Ahmad al-Khabil, also known as Abu Khawla, who was arrested in the city of Hasakeh late Sunday, the Observatory said.
The move sparked tensions that deteriorated into clashes after gunmen attacked SDF positions, added the Britain-based Observatory, which has a network of sources inside Syria.
The charges against Khabil were not immediately clear. However, the Observatory and an activist told AFP he was known to have been involved in smuggling and had amassed considerable wealth over the years.
The Deir Ezzor Military Council, one of several Arab groups affiliated with the SDF, is responsible for security in parts of Arab-majority Deir Ezzor province.
Swathes of the province are part of a semi-autonomous administration in north and northeast Syria that the Kurds carved out following the defeat of IS.
The Kurds administer the area through local civilian and military councils in an effort to stave off any Arab discontent.
"What's happening today is a settling of scores," said Omar Abu Layla, an activist who heads the DeirEzzor24 media platform.
"Corrupt commanders felt they were in danger after Abu Khawla was arrested and have tried to turn it into a tribal and Arab issue in order to protect themselves," he added, warning that the unrest could "negatively impact the region".
The SDF has not commented, but said in a statement that it had launched "an operation to bolster security" on Monday in Deir Ezzor province against IS and "criminals... involved in drug trafficking and benefiting from arms smuggling".
The operation was continuing "in order to arrest those involved in criminal activity", added the statement.
The areas where clashes have occurred are along "a known smuggling route", an SDF source said, requesting anonymity as they were not authorised to speak to the media.
Syria's war has killed more than half a million people since it broke out in 2011, escalating into a deadly conflict that pulled in foreign powers and jihadists insurgents.