WASHINGTON, July 22 (Reuters) - Israel's Arrow II missile defense system was tested at a U.S. range off the California coast on Wednesday but problems prevented the launch of the system's interceptor, the Pentagon said.

Partly underwritten by Washington, Arrow is designed to defend Israel from missile attacks from Syria and Iran, which Western nations suspect of seeking nuclear arms despite its denials.

In a test involving three U.S. missile interceptors, Arrow tracked a target missile dropped from a C-17 aircraft, the Pentagon said in a statement. The Israeli system also exchanged data on the target in real-time with elements of the U.S. missile defense system, the statement said.

"Not all test conditions to launch the Arrow Interceptor were met and it was not launched," the Pentagon said.

Other objectives were achieved and the results were being analyzed, it said.

Upgrades to Arrow, which has already been deployed at two sites in Israel, are widely seen as part of U.S. efforts to persuade the Israelis not to attack their enemy preemptively while the Obama administration pursues diplomacy with Tehran.

(Writing by JoAnne Allen; Editing by Doina Chiacu)

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