Turkish President Recep Tayyip Erdogan has accused Syrian President Bashar Assad's government of "mercilessly" killing 400,000 people and criticized Russia for backing him.

Erdogan was speaking to reporters on Tuesday before departing for Saudi Arabia for a visit that wiykd focus on Syria, the fight against terror and energy cooperation. Turkey is intensifying efforts to diversify its energy supplies since a rift with Moscow over the downing of a Russian plane.

In a comment apparently directed at Moscow, Erdogan said: "You cannot go anywhere by supporting a regime that has mercilessly killed 400,000 innocent people with conventional and chemical weapons."

Erdogan also accused countries of "adding fuel to fire" by backing Syrian Kurdish fighters, which Turkey considers as terrorists because of their links to Turkey's outlawed Kurdish rebel group.