According to Russian and Israeli forces, the Syrian regime accidentally shot down the Russian Ilyushin-20 surveillance plane off the Syria coast late Monday.

It was the worst case of friendly fire between Moscow and Damascus since Russia's game-changing military intervention in September 2015.

"The United States expresses sorrow for the death of the aircrew members of the Russian plane that was downed by Syrian regime anti-aircraft fire," Pompeo said in a statement.

It "reminds us of the need to find permanent, peaceful, and political resolutions to the many overlapping conflicts in the region and the danger of tragic miscalculation in Syria's crowded theater of operations."

Russian President Vladimir Putin said the shoot-down, using the Russian-made S-200 air defense system, was the result of "tragic accidental circumstances."

Israel has expressed "sorrow" for the Russian deaths, but insisted the Russian plane had been felled by "extensive and inaccurate Syrian anti-aircraft (surface-to-air missile) fire."

The deadly chain of events started when Israeli missiles struck the coastal region of Latakia on Monday.

Israel confirmed that it had targeted a Syrian military facility where weapons manufacturing systems were "about to be transferred on behalf of Iran" to Lebanese Shiite group Hezbollah.

The Russian military accused Israeli pilots of using "the Russian plane as a cover, exposing it to fire from Syrian air defenses," a charge Israel denied.

Pompeo added that the shoot-down underlined the "urgent need to resolve the Syrian conflict" in accordance with UN resolutions and "to end Iran's provocative transit of dangerous weapon systems through Syria, which are a threat to the region."