Intelligence sources tell Sky News chemical weapons could fall into terrorist hands if President Bashar al-Assad falls and Israel may go to war to prevent this "doomsday" scenario • "We would have to pre- empt it in order to prevent it," former Mossad head Danny Yatom says, referring to threat of Hezbollah obtaining chemical weapons • Syrian ambassador to Iraq defects.

Syria´s chemical weapons could end up in the hands of terrorist groups if President Bashar al-Assad´s regime falls, and concerns are increasing that Israel may go to war against Syria to prevent this "doomsday threat," Sky News reported on Thursday, quoting Middle Eastern and other intelligence sources.

The sources say Syria possesses the biggest stockpile of nerve gases VX and Sarin, as well as mustard gas, in the Middle East.

A Sky News investigation revealed four sites in Syria where the chemicals are produced: Hama, Latakia, Al Safira near Aleppo, and at the Centre D´Etude et Recherche Scientifique laboratories in Damascus.

Storage sites have also been identified at Khan abu Shamat, Furqlus, Hama, Masyaf, Palmyra, according to the Sky News report.

Intelligence sources believe biological weapons are being stored in the Syrian town of Cerin, and that there are several "dual use" civilian pharmaceutical laboratories that are capable of producing bio-weapons such as botulism and anthrax, Sky News reported.

Al-Qaida-linked organizations that are known to be operating inside Syria have urged members or followers to try to seize Syria´s chemical weapons.

Much of the unrest has centered on the towns of Hama, Latakia and in Damascus suburbs, making storage and production sites of chemical weapons there subject to break-ins by rebels.

The deadly chemicals have been successfully "weaponized," according to Sky News, meaning that conventional missile warheads have been mounted with delivery systems for VX gas, including Scud B, C and D missiles.

These missiles are capable of hitting any target inside Israel, Sky sources said, and "they are capable of spreading VX gas in bomblets similar to those seen in cluster munitions."

Intelligence sources estimate that Syria-backed Hezbollah, which fought a bloody war with Israel in 2006, has an arsenal of more than 40,000 missiles.

Concerns in Israel have been growing over the possibility that Assad may deliberately give Hezbollah chemical weapons, or that they could fall into the hands of other terror organizations.

In either case, this could lead to a regional war, former Mossad head Danny Yatom warned in an interview with Sky News.

"The conventional wisdom should be that we cannot exclude a non- conventional attack on Israel. We would have to pre-empt in order to prevent it. We need to be prepared to launch even military attacks... and military attacks mean maybe a deterioration to war," Yatom told Sky News.

The situation in Syria has sparked fears that a Gadhafi-style collapse of Syria into chaos would mean that chemical weapons would flow freely across the globe.

The weaponization of the chemicals means they can be moved around easily and Sky sources in the region said that the Assad regime had distributed the weapons among "dozens of different sites and into perpetually mobile columns."

Israel Defense Forces Deputy Chief of Staff Maj. Gen. Yair Naveh recently warned a private congregation at a Jerusalem synagogue that Syria´s chemical weapons posed a mortal threat to the Jewish state, Sky News reported.

"As for Syria, we all hear the news ... (if) Syrians ... behave this way to their people it is clear ... how they will behave toward us, to our sons, when they get the opportunity against us, with the largest chemical weapons arsenal in the world, with missiles and rockets that cover all of Israel," Naveh was quoted as saying.

In May, 12,000 U.S. special forces commandos spent nearly a month training for the sort of scenario existing in Syria now.

But a Pentagon study suggested that 75,000 troops would be needed to secure Assad´s chemical weapons stockpile and there seems to be little possibility of the U.S. committing that kind of force in light of tensions with Iran over its nuclear program.

"The truth is that no one has much of a clue what to do about Syria — it´s too well defended and too full of weapons of mass destruction to mean that there can be any meaningful military intervention. The Syrians may be doomed if Assad stays, and lots of others if he falls," a senior intelligence official in the region told Sky News.

Opposition: Syria´s Iraq ambassador has defected

Meanwhile, the Syrian ambassador to Iraq defected on Wednesday, denouncing Assad in a TV statement and becoming the most senior diplomat to abandon the regime during the bloody 16-month uprising.

Nawaf Fares, a former provincial governor, is the second prominent Syrian to break with the regime in less than a week. Brig. Gen. Manaf Tlass, an Assad confidant and son of a former defense minister, fled Syria last week, buoying Western powers and anti-regime activists, who expressed hope that other high-ranking defections would follow.

The high-level defections could be a sign that Assad´s tightly wrapped regime is unraveling, but it was too early to be certain. There have been thousands of defections in the past, mostly low-level army conscripts, but until now no one as senior as the general and the ambassador had fled.

In a statement broadcast on the Arabic satellite channel Al-Jazeera, Fares said he was resigning and joining the opposition. Wearing a dark suit and reading from a prepared text in what appeared to be a large office, Fares harshly criticized Assad.

"I´m announcing from this moment on that I´m siding with the revolution in Syria," he said, according to the Al-Jazeera translation into English. He called on all Syrians to abandon Assad.

"Where is the honor in killing your countrymen? Where is the national allegiance? The nation is all the people, not one person in particular," he said. "The allegiance is to the people, not to a dictator who kills his people."

It was not known where or when Fares recorded the statement.