Some 3,500 US troops and 1,000 Israeli soldiers began a large joint military drill Sunday, an Israeli military spokeswoman said.
Austere Challenge 12, scheduled to last some three weeks, simulates missiles raining down on Israel from Iran, Syria, Lebanon and the Gaza Strip to test its anti-missile batteries, dpa reported.
A US Aegis ballistic missile defence ship is also to participate from the northern Israeli port of Haifa.
The largest drill ever between the two allies costs the US 30 million dollars and Israel some 8 million dollars Some 1,000 of the US troops are participating inside Israel, while the remaining 2,500 are taking part from Europe and the Mediterranean Sea.
In a briefing last week, US Third Air Force Commander Craig Franklin would say whether the exercise was in preparation for a future strike on Iran's nuclear facilities.
Both Israel and the United States have said that the joint drill, which took more than two year to plan, is "not tied to any particular world event."
Israel Sunday also began a unrelated, five-day national exercise, Turning Point 6, practicing its response to earthquakes.