TEL AVIV - A major air defense exercise launched with Israel this week will help the United States craft its European missile shield, a U.S. commander said Thursday.

Signaling the strength of their alliance against what they say is a threat from Iran's nuclear program, Israeli and U.S. forces launched a two-yearly drill Wednesday. Known as Juniper Cobra, it includes target practice against missiles, both real and in computer-simulated exercises.

Featuring in the three weeks of maneuvers is Aegis, a U.S. Navy anti-missile system that the administration of President Barack Obama plans to deploy in the eastern Mediterranean as the first part of a missile shield for Europe announced last month.

Aegis is made by Lockheed Martin Corp and fires the Standard-Missile 3, which is made by Raytheon Co.

In this series of exercises we continue to advance our understanding of the art and the science of ballistic missile defense, Rear Admiral John Richardson, the U.S. officer overseeing Juniper Cobra, told reporters in Tel Aviv.

This exercise is not directly related to recent announcements about ballistic missile defense in Europe, but the lessons and the insights that we gain from this exercise will certainly relate to developing that capability.

The drill comes as world powers try to talk Iran into curbing uranium enrichment, a process with bombmaking potential.

Tehran denies seeking nuclear weapons but the secrecy around its plans and its vituperation of the Jewish state has stirred fears of a preemptive Israeli strike -- something publicly opposed by Washington, which cites Iran as the main reason for the planned European anti-missile system deployment.

Both Richardson and his Israeli counterpart in Juniper Cobra, Brigadier-General Doron Gavish, declined to be drawn on whether Iran was the main adversary envisaged in the exercise.

They said it served to test the interoperability of Aegis and other American anti-missile systems like THAAD and Patriot with Israel's Arrow II interceptor, and to establish procedures for the emergency U.S. enhancement of Israeli forces.

None of the American materiel used in the drill will remain in Israel after it winds up in mid-November, they said. But the United States does have a small military garrison at a strategic radar, X-band, stationed in Israel's southern Negev desert.

The Israel Defense Force can defend Israel alone, Gavish said. But it is good to know that U.S. capabilities are available.

(Writing by Dan Williams; Editing by Alastair Macdonald)