The US-backed Syrian Democratic Forces kicked off on Tuesday the final stage in its battle to expel the ISIS terrorist group from eastern Syria.
Backed by the US-led coalition, the Kurdish SDF have driven ISIS out of large parts of the country.
ISIS has retained a presence in a few areas of the country, including in the eastern oil-rich province of Deir Ezzor near the border with Iraq.
The SDF's Deir Ezzor Military Council on Tuesday said it would press its efforts to oust ISIS from remaining areas.
"Our forces with the forces of the international coalition have started the last stage" of the anti-ISIS campaign, it said in a statement.
"Our forces will liberate these areas and secure the Iraqi border once and for all," the military council announced at the Al-Tanak oilfield east of the Euphrates.
The United States confirmed the start of the military operation.
ISIS holds dozens of villages in eastern Syria, from the eastern banks of the Euphrates River that cuts across Deir Ezzor to the border with Iraq, and in the south of the adjacent province of Hasakeh.
The US State Department said later that the coalition and its "partners, including the Syrian Democratic Forces, are launching operations to liberate the final ISIS strongholds in Syria".
"The fighting will be difficult, but we and our partners will prevail... The days of ISIS controlling territory and terrorizing the people of Syria are coming to an end," it said in a statement.
Deir Ezzor Military Council head Ahmed Abu Khawla told AFP there was a "shared operations room with Iraqi forces".
The US-led coalition including French forces had increased their numbers and would support the SDF in "the final stage" of their operation, he said.
French special operations forces arrived in Syria last month to help boost US-led efforts against ISIS, US Defense Secretary Jim Mattis said last week.
Turkey’s offensive to expel the People’s Protection Units (YPG) from Afrin - where the United States has no presence - led to a pause in the campaign against ISIS, the Pentagon has said.
Turkish forces captured Afrin in March.
Abu Khawla said SDF forces that had fought in Afrin have now returned to the east. The assault on Afrin “distracted from eliminating ISIS.”
“It had a very big and wide impact on the liberation, which was stalled for months.”
The United States will also work with Turkey, Israel, Jordan, Iraq and Lebanon to secure their borders from ISIS and will seek further contributions from regional partners and allies to stabilize liberated territories, the State Department said.
ISIS swept across large parts of Syria and neighboring Iraq in 2014, declaring a so-called "caliphate" in areas they controlled.
But ISIS has since lost much of that territory to various offensives in both countries.
