WASHINGTON (AP) — The Federal Aviation Administration issued a notice Monday barring flights of U.S. planes over Syria, citing extremist groups equipped with anti-aircraft weapons that could pose a serious threat.

The latest notice replaces one that strongly advised U.S. flight operators against flying over Syria and urged them to contact the agency before flying there.

The FAA said opposition groups in Syria have successfully shot down Syrian military aircraft.

The FAA earlier this month prohibited U.S. airlines and other commercial carriers from flying over Iraq as the U.S. launched its first airstrikes there.

Syria’s conflict has killed more than 170,000 people since March 2011. The civil war has been intensified by the rise of the Islamic State group, which controls broad areas of Syria and Iraq.

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