"The U.S. must step back from this grave mistake and not allow itself to be blackmailed by the terrorist outfit," Turkey's top diplomat said.
The deadly shelling was a reminder that the city once called "hell" by the U.N. chief was still threatened by violence a year later.
"It was all theater," said the U.S.-backed commander who has since switched his allegiance to Turkey.
Syria's war is almost over and experts say the U.S. has few options to counter what's been a major victory for Russia, Iran and President Bashar al-Assad.
Two rivals are battling ISIS in the jihadists' final stronghold of Deir ez-Zor. One seeks to return Syria to its former self; the other wants more power for Kurds.
Russian and U.S. allies are battling insurgents and jihadists trying to topple the Syrian government, but the latter wants to reshape the nation.
Syrian President Bashar al-Assad, his opposition, U.S.-backed Kurdish forces and the Islamic State militant group (ISIS) all recognized Eid al-Adha.
Once a primary recipient of CIA assistance, the Free Syrian Army has since turned on U.S. efforts to battle ISIS using Kurdish militias.
As forces supported by the U.S. and Russia defeat ISIS across Syria, Secretary of State Rex Tillerson seeks Moscow's help to prevent a new conflict.
Pro-Kurd media shared footage of Syrians burning burqas and cutting their beards after the Syrian Democratic Forces defeated ISIS in an area of Raqqa.
The Islamic State militant group killed an activist from California, a U.S. Army veteran from New York and another YPG volunteer from the U.K.
Kurdish militants are on the front lines of U.S.-led efforts to defeat the Islamic State militant group, but what happens when the battle's over?
The Russia-backed Syrian military and its allies entered ISIS-held Raqqa, where U.S.-backed forces are battling the jihadis.
The former national security adviser reportedly received $500,000 to lobby for Turkey which opposes the U.S. backing of Kurdish forces in Syria.
The U.S.-backed, majority-Kurd Syrian Democratic Forces and the Russia-backed Syrian military are separately threatening ISIS's final major strongholds.
The U.S. military killed 18 fighters of the allied Syrian Democratic Forces in a friendly fire incident in northern Syria.
Ryan Lock, 20, died in December 2016 during a battle for the ISIS stronghold of Raqqa in Syria.
The Turkish president rejected claims that Kurdish forces have withdrawn.