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Why would Israel attack Syria?
As the uprising against Syrian President Bashar al-Assad nears its third year, concern has been expressed about the possibility of widespread chaos resulting in the loss of control - or deliberate dissemination - of weapons of mass destruction, such as chemical arms Damascus is said to possess. Israeli Prime Minister Benjamin Netanyahu is reported to have threatened to take action in the event of a loss of control by Mr Assad. Israeli military intelligence is thought to be monitoring the area via satellite for any movement of weapons outside Syria's borders. Israel fears that Syria may unravel in such a way as to seek to destabilise the entire region.
Of particular concern in Israel is Damascus's support for Lebanon's Hezbollah. Israeli officials believe that Hezbollah's arsenal has improved to include thousands of rockets and missiles and the ability to strike almost anywhere inside Israel. A former Israeli intelligence official, Amnon Sofrin, says Hezbollah is known to have been storing some of its more advanced weapons in Syria and will seek to move everything it can into Lebanon. "As soon as these weapons reach Lebanon, they are swallowed up in secret underground stockpiles. Looking for them will be like searching for a needle in a haystack," Israeli defence analyst Alex Fishman said in the Yedioth Ahronoth newspaper. "If chemical weapons are brought into Lebanon, Israel will probably not hesitate - and will attack," Mr Fishman said. Israeli Home Front Defence Minister Avi Dichter said on Tuesday that options to prevent Syria from using or transferring the weapons included deterrence and "attempts to hit the stockpiles".
On Sunday, Israel moved a battery of its Iron Dome defence system to the northern city of Haifa. Matthew Levitt, a former US intelligence official who works at the Washington Institute for Near East Policy, said Israel flew reconnaissance flights over Lebanon "with impunity right now".
The SA-17 is a modern Russian system which comprises four missiles on a tracked launcher, coupled with an associated radar system. This would be a significant enhancement of Hezbollah's capabilities - it would reduce Israel's ability to conduct aerial intelligence, Mr Levitt says. Some four years ago, the then Israeli government of Prime Minister Ehud Olmert warned that it would not tolerate what it called "game-changing" weapons being transferred to Hezbollah. This included sophisticated anti-aircraft missiles, anti-shipping missiles, or long-range ground-to-ground missiles. The Lebanese authorities clearly object to Israel's almost routine infringement of their airspace but have very little ability to do much about it. The SA-17 could change that.
Has Israel carried similar strikes before?
This week's alleged Israeli strike is the first inside Syria since September 2007, when Israeli warplanes were suspected to have destroyed a site that the United Nations nuclear watchdog, the IAEA, said was likely to have been a nuclear reactor. Syria denied the claim, saying the building was a non-nuclear military site. Israel also never admitted bombing the site near Deir Ezzor in eastern Syria. Analysts say the ambiguity allowed Damascus to withstand any pressure to retaliate. In 2006, Israeli jets flew over Mr Assad's presidential palace in a show of force after Syrian-backed Palestinian militants of Hamas in the Gaza Strip captured an Israeli soldier. And in 2003, Israeli warplanes attacked what they described as the Ein Saheb training camp, 22km (14 miles) outside Damascus, which it said was used by several militant Palestinian groups, including Hamas and Islamic Jihad. It came in response to an Islamic Jihad suicide bombing in the city of Haifa that killed 21 Israelis. Syria vowed to retaliate for both attacks, but never did.
Syria and Israel have been technically in a state of war since the creation of the state of Israel in 1948. The main grievance is over Israel's occupation of the Golan Heights in 1967. Syria has been demanding the area back as part of any peace deal. But the border area has been quiet and Damascus has never retaliated to Israeli attacks.
Are there fears of the Syrian war spreading in the region?
Israel fears that the impact of the Syrian civil war may provoke a wider confrontation with Iran and Hezbollah. In November 2012, Israeli tanks hit a Syrian artillery unit after several mortars fell on Israel's side of the border. But analysts say that, despite the increased tensions, it is unlikely that Damascus will retaliate for the alleged Israeli strike - or strikes. "It is necessary and correct to prepare for deterioration - that scenario exists," Danny Yatom, former head of Mossad, Israel's intelligence agency, told Ynet news. "But in my assessment, there will not be a reaction, because neither Hezbollah nor the Syrians have an interest in retaliating." President Assad was "deep in his own troubles", Mr Yatom said, "and Hezbollah is making a great effort to assist him, in parallel with its efforts to obtain weapons, so they won't want to broaden the circle of fighting".
This alleged Israeli operation will serve as a warning to the Syrian authorities and to Hezbollah. Syria has been covertly arming Hezbollah for many years. Hezbollah, along with Iran, is among the few friends the Syrian leadership has left. President Assad may be in some difficulty at home, but if his public utterances are anything to go by, he believes he can ride out the storm and having a well-armed ally in Lebanon may suit his longer-term strategic goals.
Hezbollah says it has replenished and increased its weapons stocks since the 2006 war with Israel. Hezbollah - like Israel - clearly believes that there will be a new round of fighting between them, says the BBC's diplomatic correspondent Jonathan Marcus. It wants to bolster its arsenal, especially in areas like air defence where it remains relatively weak. Quite how it may respond is unclear. Last July's attack on an airport bus carrying Israeli tourists in Bulgaria suggests that if there is to be a response it might be indirect - against Israeli or Jewish targets abroad, rather than across Lebanon's own frontier with Israel. Either way, the situation in the region has become even more complex - the ramifications of the Syrian crisis thrown ever more starkly into relief, our correspondent says.
