The United States and Israel will hold a major missile defense exercise in Israel this month, sending a message of close cooperation as both countries weigh their options over Iran’s nuclear program.

The three-week exercise, the largest the allies have ever held, will simulate a variety of long and short-range missile attacks that Israel could face during a regional conflict, said the commanders in charge.

Asked whether it sent a message to Iran, which has warned of an all-out war should Israel try to strike its nuclear facilities, Israeli Brigadier General Nitzan Nuriel said: “Anybody can get any type of message from this exercise.”

“The fact that we are practicing together and working together is a strong message by itself,” Nuriel said during a conference call with reporters.

Offering a more guarded response, his U.S. counterpart, Lieutenant General Craig Franklin said the exercise, “is not there to send a message”, adding that it has been in planning for more than two years.

“This exercise will improve the cooperative missile defense of Israel and will promote regional stability and help ensure our military edge,” he said.

More than 3,500 U.S. personnel will take part in the drill, about 1,000 of them in Israel, Franklin said, putting a total price tag on the exercise at $60 million.

The weapons will include U.S. Patriot missile batteries and an AEGIS ballistic missile defense ship, along with the multi-tiered missile defense system that Israel has been developing. All but one of the launches will be simulated.