Israeli Prime Minister Benjamin Netanyahu
Israeli Prime Minister Benjamin Netanyahu has told the BBC that Israel has a right to prevent weapons from falling into the wrong hands in Syria.
He said that if terrorists seized weapons such as anti-aircraft and chemical weapons they could be "game changers" in the region.
Israel has said its policy is not to get involved in the Syrian conflict.
But in recent months it has retaliated following Syrian fire into Israeli-controlled areas in the Golan Heights.
Israel first occupied the Golan Heights in 1967 and later annexed the territory in a move that is not internationally recognised.
Since the uprising against President Bashar al-Assad began, there have been growing calls for the international community to arm the rebels.
But there is increasing concern that Islamist militants fighting alongside other rebel groups could use such weapons to further their own causes.
Netanyahu, in an interview with the BBC's Lyse Doucet, said Israel's concern was "which rebels and which weapons?"
"The main arms of concern to us are the arms that are already in Syria - these are anti-aircraft weapons, these are chemical weapons and other very, very dangerous weapons that could be game changers," he said.
"They will change the conditions, the balance of power in the Middle East. They could present a terrorist threat on a worldwide scale. It is definitely our interest to defend ourselves, but we also think it is in the interest of other countries."
Asked if Israel would adopt a more aggressive military stance in Syria, Netanyahu said: "We are not aggressive. We don't seek military confrontation, but we are prepared to defend ourselves if the need arises and I think people know that what I say is both measured and serious."
Netanyahu would not confirm what was widely believed to have been an Israeli air strike on a suspected Syrian government weapons convoy in January.
It was reported that the convoy had been heading for Hezbollah fighters in Lebanon.
Netanyahu was in London to attend Baroness Thatcher's funeral and also held talks with UK Prime Minister David Cameron.
Earlier, President Assad accused Western countries of backing al-Qaeda in his country.
He warned that they would pay a heavy price in Europe and the US as militants became emboldened.