Russia will brief the United Nations Security Council on Tuesday at 3 pm GMT about the results of the Tehran summit it held with Iran and Turkey on the fate of Syria's Idlib province.

The council will meet at Russia's request to hear the briefing as Syrian forces, backed by Russia and Iran, are preparing for an all-out military assault on the rebel-held province.

The United Nations has warned of a major humanitarian catastrophe if the offensive takes place in the enclave where some three million people live - about half of whom have already been displaced in the seven-year war.

On Friday, the presidents of Iran, Russia and Turkey failed to agree during the Tehran summit on how to stave off military action on the northwestern province.