JERUSALEM — The Syrian armed forces fired antiaircraft missiles at Israeli warplanes that had struck targets deep in Syria early Friday, in what appeared to be the most serious clash between the militaries since the start of the Syrian civil war six years ago.

The Syrian army’s General Command asserted that its forces downed one of four Israeli aircraft that conducted operations around the ancient city of Palmyra, and hit another, the Syrian state news agency SANA reported. The Israeli military denied that claim, saying in a statement that “at no point was the safety of Israeli civilians or the IAF aircraft compromised,’’ referring to the Israeli air force.

The Syrian missiles set off Israeli air raid sirens and aerial defense systems in the Jordan Valley, and the Israeli military said its Arrow air defense system had intercepted one of the missiles — the first confirmed operational use of that anti-missile system.

New York Times