AFP - Turkey's prime minister on Sunday delivered his most virulent attack so far on Bashar al-Assad, calling the Syrian president a "butcher" and warning that he will be held to account for the deaths of tens of thousands of his citizens.

"If God permits, we will see this butcher, this murderer receive his judgement in this world ... and we will praise (God) for it," Recep Tayyip Erdogan said.

"You will pay a very, very heavy price for showing your courage to the babies in the cradle, the courage you cannot show others," he told a cheering crowd of lawmakers and party activists in a town near Ankara.

Erdogan's harsh words came after reported Israeli air strikes on a military target near Damascus, which Israeli sources said hit Iranian weapons destined for the Lebanese militant group Hezbollah, an ally of the Syrian regime.

Ankara's first open challenge to Damascus to respond to Israeli operations came in February, when the Jewish state implicitly confirmed that its warplanes had hit a military complex near Damascus.

Turkish Foreign Minister Ahmet Davutoglu then mocked the Syrian army for its failure to retaliate.

"Why doesn't it throw even a pebble?" he said.

Ankara cut contact with Damascus after its calls for a peaceful resolution of the conflict, which is now in its third year and has killed more than 70,000 people, went unheeded.

Turkey has sided with the rebels fighting to topple Assad's regime, taken in around 400,000 refugees as well as army defectors and repeatedly called on the international community to act on the unfolding crisis.