The Russian, Iranian and Turkish foreign ministers had met in the Kazakh capital of Astana, and the focus of their consultations was Eastern Ghouta, an opposition enclave just outside Damascus, which the regime of Syrian President Bashar al-Assad began pounding a month ago.

The Astana meeting was to lay the ground for a summit involving the presidents of the three countries in Istanbul on April 4.

Speaking after the talks, Russian Foreign Minister Sergei Lavrov accused the West of shielding terrorists and even trying to "preserve their combat potential"

Both Moscow and Tehran back Assad, but Ankara has called for an to the siege in Eastern Ghouta, in which nearly 1,260 civilians have been killed, a fifth of them children, since it began on February 18.