A shell explodes in the town of Yabroud, near the Syrian capital Damascus, purportedly on Friday.

Reuters cannot independently verify the authenticity of this clip which was posted on a social media website.

Another clip shows the aftermath of air strikes in Douma, just outside Damascus.

As the violence in Syria intensifies, Israeli Prime Minister Benjamin Netanyahu said Israel was preparing for every scenario - including the possibility that advanced weapons supplied by Russia to Syria ending up in the wrong hands.

Netanyahu said Israel was closely following the developments in Syria at a particularly sensitive period for the Middle East.

He said his government was acting in a "responsible, determined and measured' manner to ensure Israel's security and prevent weapons leaks to 'Hezbollah and terror organisations'.

Israel has neither confirmed nor denied reports that it attacked Iranian supplied missiles stored near Damascus earlier this month that