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US-backed Syrian forces set sights on valley north of Raqqa

  • This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces carrying the coffins of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, during their funeral procession, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)

    This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces carrying the coffins of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, during their funeral procession, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)  (The Associated Press)

  • This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces carrying the coffins of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, during their funeral procession, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)

    This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces carrying the coffins of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, during their funeral procession, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)  (The Associated Press)

  • This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces attending  the funeral procession of 18 of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)

    This photo provided by Hawar News Agency, a Kurdish-run news agency, which has been authenticated based on its contents and other AP reporting, shows fighters from the predominantly-Kurdish Syrian Democratic Forces attending the funeral procession of 18 of their comrades, who were killed Tuesday by a misdirected airstrike by the U.S.-led coalition, in Tal al-Abyad, northeast Syria, Thursday, April 13, 2017. U.S. Central Command said coalition aircraft were given the wrong coordinates by their partner forces, the Syrian Democratic Forces, for a strike intended to target Islamic State militants south of their Tabqa stronghold. (Hawar News Agency via AP)  (The Associated Press)

U.S.-backed Syrian Kurdish forces say they have entered the fourth stage of their campaign to capture the Islamic State group's de facto capital Raqqa with an advance on the militants in a valley north of the city.

The Syrian Democratic Forces, which include Arab fighters, say they are working to clear the militants out of the Jalab Valley, north of Raqqa. An estimated 300,000 people are in the city.

The SDF says it wants to isolate Raqqa before attacking it. Their closest position is within 8 kilometers (5 miles) northeast of the city. But the countryside south of Raqqa is still under IS control.

It is unclear how many stages are planned for the SDF campaign.