Tests of a missile-defense system meant to shield Israel from Iranian attack were aborted over the past week on three occasions because of various malfunctions, Israeli defense officials said Thursday.

In the latest case, an upgraded version of the Arrow II — a system being developed by state-run Israel Aerospace Industries Ltd. and Chicago-based Boeing Co. — was tested off the coast of California on Wednesday, they said.

But communication glitches between the missile and the radar led U.S. defense officials to abort the test before an intercepting missile could be fired, they said.

They spoke on condition of anonymity because they were not authorized to disclose details of the tests, which were carried out in the U.S. because that would allow for greater distances than would be possible in Israel, Defense Ministry spokesman Shlomo Dror said.

The Arrow is part of a multilayered missile defense system Israel is working on to protect it from all forms of attack, ranging from short-range rocket fire from Lebanon and the Gaza Strip to longer-range threats from Iran.

Dror said tests of the same Arrow system in Israel earlier this year were "very successful." He said malfunctions of systems still in their experimental stage were to be expected and said other tests were called off on Friday and Monday.

The defense officials said the improved Arrow II was meant to intercept a dummy Iranian Shihab missile, which is capable of carrying a nuclear warhead. But U.S. officials blocked the launch of an intercepting missile because of the communications glitch, the Israelis said.

Iran's Shihab-3 has a range of up to 1,250 miles (2,000 kilometers), putting Israel well within striking distance.

Isaac Ben-Israel, a retired general and weapons expert, said the interceptor wasn't fired because it is too expensive to use in a test that isn't expected to go according to plan. He said such glitches are common when developing new systems and he did not consider it a significant setback.

"I expect that within a short period of time, after they determine exactly what happened, they will repeat this experiment and then we will know if it works or not," Ben-Israel said.

Israel sees Iran as its biggest threat, because of its nuclear program and development of medium-range ballistic missiles. Those fears have been compounded by Iranian President Mahmoud Ahmadinejad's persistent anti-Israeli rhetoric.

Israel, like many in the international community, rejects Iran's claims that its nuclear program is only to produce energy.

An operational version of Arrow II is partially deployed, and the U.S. and Israel are in the preliminary stages of developing an upgraded Arrow III.

The homegrown "Iron Dome" system is designed to bring down short-range rockets of the kind Palestinian and Lebanese militants use. Last week, Israeli officials reported a successful live test of the system.

The Arrow project was spurred largely by the failure of the U.S. military's Patriot missiles to intercept Iraqi Scud rockets that struck Israel in the 1991 Gulf War.