The United States announced it is sending an advanced anti-missile system and a number of troops to Israel, deepening America’s involvement in the spiraling conflict as the region readies for Israeli retaliatory strikes against Iran.

The decision was announced just hours before a Hezbollah drone strike on an Israeli base killed four soldiers and wounded 61 others without triggering an alert.

The Terminal High Altitude Area Defense, known as THAAD, usually requires about 100 troops to operate, and has six truck-mounted launchers, with eight interceptors on each launcher, as well as a powerful radar. It is capable of intercepting ballistic missiles at ranges of 100 to 125 miles.

Retired Brig. Gen. Zvika Haimovich, former head of the Israeli Air Defense, said Israel expects an even bigger barrage of missiles from Iran in “the next phase,” after Tehran fired more than 180 missiles at Israel on Oct 1.