"The U.S. Embassy has received reports that extremist groups may be planning an attack against the Syrian Interim Government building," the statement said.
"We remind U.S. citizens that the situation in southeast Turkey, while usually calm, can change without warning and U.S. citizens should avoid traveling in areas close to the Syrian border," it said.
The body was formed by the Western-backed National Coalition for Syrian Revolutionary and Opposition Forces in November 2013. Early this year it set up its headquarters in Gaziantep, a province bordering Syria.
It exists to provide local services and support in rebel-held areas in Syria but fighting, political squabbling and the reluctance of donors to support a partisan body have limited its influence.
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