Those who died south of the city of Tabqa were members of the Syrian Democratic Forces (SDF), said the Pentagon. Central Command said the strike was launched Tuesday.
The airstrike was carried out south of Tabqa, a focus area for the coalition as it closes in on the ISIS heartland of Raqqa.
Several nations have lent their air power to the coalition to defeat the jihadist group. Anti-ISIS forces on the ground are preparing to mount an offensive against Raqqa, supported by USA and coalition air power as well as US special forces.
Sergey Lavrov said Thursday that inspectors from the Organization for the Prohibition of Chemical Weapons should both visit the Syrian air base, which the US said had served as a platform for the attack, and the town of Khan Sheikhoun that was hit to get a full and objective picture. U.S. Ambassador to the U.N. Nikki Haley said the veto left Moscow, a key ally of the Syrian government, with "a lot to prove".
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At a later congressional hearing, Comey said he had "no information" to support the president's assertions. Many Clinton campaign officials blame Comey's late action for swaying the election to Trump.
A British delegation at a behind-closed-doors meeting of the worldwide chemical weapons watchdog says in a tweet that the organization's director general has said that its investigators already are testing samples from a suspected deadly chemical weapons attack in Syria's Idlib province.
The report comes one day after Russian Federation vetoed a Western-backed U.N. Security Council resolution demanding a speedy probe into the April 4 attack on the rebel-held town of Khan Sheikhoun, which has been widely blamed on government forces.
The Organization for the Prohibition of Chemical Weapons has a standing fact-finding mission on Syria to investigate alleged chemical weapons attacks, but does not apportion blame.
The Syrian Democratic Forces has been battling ISIS and other fundamentalist groups in Syria's civil war, with the goal of establishing a secular and democratic state.
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But the fourth phase of the campaign aims to clear Islamic State pockets from the countryside north of the city, the SDF statement said.
It is unclear how many Islamic State insurgents remain in Tabqa, but Rasho said they were "few", based on the estimates of residents fleeing the city.
Officials in the Kurdish YPG militia, a powerful component of the SDF, said last month that assaults on Raqqa city itself would start in early or mid-April.
Flight to safety lifts yen, gold and bonds
It was a similar story for the pound, which retreated to a near five-month low of 136.85 yen but edged up against the dollar. The Australian dollar dipped below the key $0.75 level against the greenback, wallowing near three-month lows.