Shimon Peres, the Israeli president, says that Syrian President Bashar al-Assad has become a "murderer" of his people and that they should overthrow his government.

"Their president, who is supposed to be the father of their nation, became their murderer," Peres told reporters during a joint press conference with visiting German President Joachim Gauck.

"Nobody can remain indifferent to it," the Nobel peace laureate said. "The reactions until now have been declarations; unfortunately, declarations don't stop murders and assassinations. I think the time has come to help the Syrians achieve peace and regain their freedom."

The massacre in Houla would appear to have brought an end to Israel's long official silence on events taking place across its northern border.