U.S.-backed forces are preparing for the third phase of an assault to retake the city of Raqqa from Islamic State in Iraq & Syria (ISIS) militants, Reuters reported Saturday.

The Syrian Democratic Forces (SDF) said on Saturday it was launching the campaign with "increasing support from the international coalition forces through guaranteeing air cover for our forces' advances, or via the help provided by their special teams to our forces on the battle ground,” as reported by the news service.

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A commander told Reuters that forces advanced several kilometers as they seek to take territory east of Raqqa to cut off the highway leading to the Deir al-Zor province, which is largely under control of ISIS militants.

The SDF began the effort to take the ISIS stronghold in November. Earlier phases included efforts to take areas west and north of the city.

The United States last month supplied the SDF with armored vehicles as it prepared for the assault, according to a January Reuters report.

ISIS took control of Raqqa in January 2014, making the city its de-facto capital in Syria.

The Washington Post reported on Thursday that the Obama administration in its final months had been preparing a campaign to re-take the city, but officials in the incoming administration said they wanted to make the decision.

The Obama administration handed the details, which included arming Kurdish fighters, over to the Trump Administration just before leaving office. The new national security team declined to move forward with the plan.

President Trump Donald John TrumpTrump says he doesn't think he could've done more to stop virus spread Conservative activist Lauren Witzke wins GOP Senate primary in Delaware Trump defends claim coronavirus will disappear, citing 'herd mentality' MORE last month signed an executive order calling for military leaders to devise a plan within 30 days to defeat ISIS.