Watch: Video testimonies of American and British volunteer fighters killed in Syria

Two Americans and a Briton died fighting alongside Syrian Kurdish forces as they battle to oust the Islamic State group from its stronghold in Raqqa, Syria, the forces said Tuesday.

The three men volunteering with the Kurdish People's Protection Units (YPG) appear to be the first foreign volunteers to have died since fighting began inside the northern Syrian city. 

In a statement on its website, the YPG said Americans Robert Grodt and Nicholas Warden and Briton Luke Rutter were among six "martyrs" on the Raqqa front, without saying where exactly they died.

In tweets on Tuesday, the YPG said Rutter and Warden were "martyred in action" on July 5 and Grodt died the following day.

The YPG is the key component of the US-backed Syrian Democratic Forces alliance of Kurdish and Arab fighters partnering with the US-led coalition against ISIS.

On Nov. 5, 2016, the SDF launched an offensive dubbed "Wrath of the Euphrates" to retake Raqqa, and after months of fighting in the surrounding province, they entered the city in June for the first time.

In a video posted by the YPG on social media, Rutter appeared on camera in military fatigues, holding a gun, and said he had received training and Kurdish language lessons since arriving in Syria in March this year.

"I lied to people I care about to come here," he said.

"Apart from that I don't regret my decision and I hope that you respect it."