Russia and Iran have offered military and diplomatic support to the Syrian government as it tries to stanch a major rebel advance.

In just a few days, a patchwork of rebel forces has seized control of a broad stretch of land in the west and northwest of Syria. But it’s unclear just how much support Syria’s weakened allies can provide.

The loss of Aleppo to Islamist rebels represents a stunning defeat for the Syrian regime, highlighting its dependence on enfeebled allies.