Syrian state television said on Monday an airstrike by a U.S.-led coalition had killed 18 Iraqi refugees at a school in eastern Syria, but the coalition denied it.
The state television report said the strike took place in a village in Hasaka province between the Euphrates river and the Iraqi border, an area where a U.S.-led coalition is supporting local fighters against Islamic State.
A spokesman for the coalition, Col. Sean Ryan, said the report was false, adding "we are not tracking any coalition strikes today in Hasaka injuring or killing civilians".
A war monitor, the Syrian Observatory for Human Rights, said the U.S.-backed fighters had captured the village in fighting, but did not know if civilians had been killed by a strike there.
Last week the rights group Amnesty International issued a report saying there was evidence the U.S.-led coalition broke international humanitarian law with some of its strikes in Raqqa last year by endangering the lives of civilians.
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The coalition rejected that, saying it applies "rigorous standards to our targeting process and takes extraordinary efforts to protect non-combatants".
Fighting has intensified east of the Euphrates in recent weeks since the Syrian Democratic Forces, an alliance of Kurdish and Arab militias, resumed its campaign against Islamic State.
Backed by the coalition, the SDF took swathes of northern and eastern Syria from Islamic State last year, including the jihadists' Syrian capital of Raqqa.
However, with some desert areas east of the Euphrates still in Islamic State's hands, it paused its campaign in February when Turkey attacked the Afrin area in northwest Syria, held by the SDF's strongest component, the Kurdish YPG.
Fighting has also flared west of the Euphrates in recent weeks in desert areas the Syrian government reclaimed from Islamic State last year, after the group launched a series of attacks.
The Observatory said late last week the jihadists had attacked Albu Kamal, the last significant town the group had held in Syria last year before pro-government forces seized it.
On Sunday, pro-government media issued a video online showing a Syrian army offensive in a desert area southeast of Damascus against Islamic State fighters there.