DUBAI: Two senior officers from Iran's Revolutionary Guards were killed fighting ISIS in Syria, Iran's Tasnim news agency reported, ahead of a planned offensive by Syria's army backed by Tehran.

Major General Farshad Hasounizadeh and Brigadier Hamid Mokhtarband, commanders in the Islamic Revolutionary Guards Corps (IRGC), died in action on Monday, Tasnim said late on Tuesday. It did not say where they were fighting.

Iran has sent thousands of troops into Syria in recent days to bolster a planned ground offensive against insurgents in Aleppo by the Syrian army, which will also be supported by Russian airstrikes, two senior regional officials told Reuters.

The government of President Bashar Assad has been strengthened by two weeks of Russian airstrikes that the Kremlin says are targeting ISIS. The United States says they have also targeted other rebel groups.

Another senior Revolutionary Guards commander, Hossein Hamedani, was killed last week while advising the Syrian army near Aleppo.

Tehran is Assad's main regional ally and has provided him with military and economic support during Syria's civil war, now in its fifth year.