Ammon News - JERUSALEM (Reuters) - Israel has asked Russia not to sell Syria an advanced air defense system which would help President Bashar al-Assad fend off foreign military intervention as he battles a more than two-year-old rebellion, Israeli officials said on Thursday.

Citing U.S. officials, the Wall Street Journal reported on Wednesday that Israel had told Washington that Syria had already began payments for a $900 million purchase of the S-300 and an initial delivery was due within three months.

The S-300 is designed to shoot down planes and missiles at 125-mile (200-km) ranges. It would enhance Syria's current Russian-supplied defenses, which did not deter Israel from launching devastating air strikes around Damascus last weekend.

"We have raised objections to this (sale) with the Russians, and the Americans have too," an Israeli official told Reuters.

There was no immediate comment from Moscow or Damascus.

In 2010, Russia backed out of a tentative S-300 sale to Iran that had been in the works for years. Russian President Dmitry Medvedev cited U.N. sanctions imposed that year over Iran's defiance of international demands to curb its nuclear program.

Israel and the United States, which threaten military attacks on Iranian nuclear facilities if diplomatic alternatives fail, had lobbied Moscow to the deal with Tehran.

ISRAEL ATTACKS

Israel bombed sites near the Syrian capital on Friday and Sunday which intelligence sources said held Iranian-supplied missiles destined for Hezbollah guerrillas in neighboring Lebanon. The heavy presence of Israeli warplanes in Lebanese airspace suggested they may have eluded Syrian defenses by launching long-range missiles across the border at the targets.

Assad accused his Israeli foe of attacking Syria in order to support the insurgency there - an allegation denied by Israel, though, like Western powers, it has urged his ouster.

Russia, however, has balked at such calls. It voiced "particular alarm" at Israel's air strikes, seeing a possible precursor for Western military intervention against Assad.

Robert Hewson, an IHS Jane's air power analyst, said that were Syria to receive the S-300 it would probably take several months to deploy and operate the system. But he suggested it would not pose a big challenge for Israel's hi-tech air force.

"It's a fairly well-established, fairly well-understood system, so there is a corpus of knowledge, particularly among Israel's friends, about how to deal with this system," he said.

Once activated, the S-300 could easily be spotted thanks to its distinctive radar signal, Hewson said, "and from there it's a fairly short step to taking it out. It's not a wonder-weapon."

Cyprus bought the S-300 and eventually positioned it on the Greek island of Crete. Israel, which has close ties with Nicosia and Athens, may have tested its jets against that S-300's capabilities during Mediterranean overflights, Hewson said.