(CBS News) Iran has long denied that it is directly involved in the Syrian civil war, but that is a lie. CBS News has photographic proof that Iran's elite Revolutionary Guard is engaged in combat alongside Syrian government forces to put down a popular revolt that began two-and-a-half years ago.
Why does it matter? A human rights group reported Thursday that the death toll in the war has now reached 120,000, including nearly 43,000 civilians. And the State Department told CBS News one-third of Syrians have now lost their homes - the equivalent of 100 million Americans being displaced. We've seen rare pictures of Iranian advisers in Syria before, but we haven't seen them fighting like this: Members of the elite Revolutionary Guard on the frontlines of Syria's civil war.
The video was shot by Hadi Baghbanis, a Tehran cameraman who was invited to film a guard unit under the command of 33-year-old Mohsen Ismail Haideri, who offers a guided tour on camera of his battle sector on the outskirts of Aleppo.
Haideri has spent eight of the past 18 months here - and the local kids now know he's good for a handout of candy.
In this Revolutionary Guard unit, there are about a dozen soldiers, specialists in communications and weapons and even a cleric to lead the soldiers in prayer.
The unit lives in a former school that now functions as their base. Haideri, relaxed and confident, describes how just 24 hours ago, his unit fought off a rebel attack. "One hundred and fifty of them came here in vehicles," he said, "but we hit back and killed 10 or 15. They had to retreat."
The Revolutionary Guard's main job is to make hardened fighters of these Syrians - civilian men armed by President Bashar Assad to beef up the over-stretched military. And the Iranians are starting with the basics.
"Get your head down," said the lieutenant to a man standing on a tank. "You'll get it blown off if you stand up there."
In one scene, the Iranians are taking the Syrians out into rebel territory on a reconnaissance mission, but what the men don't know as they get into position is that the rebels have spotted them and they have prepared an ambush.
Once the rebels start shooting, the Iranians realize they are in trouble - running out of ammunition and pinned down by enemy fire outflanked.
Suddenly the camera goes to black. The cameraman and Commander Haideri were killed, and both were mourned at elaborate funerals back in Iran.
As for what difference the Iranian force made to the Syrian dictatorship in its fight against the rebels, it's been decisive. Not only have Iranian-backed militias turned the tide in the government's favor in several key battles, but also this year alone Iran has lent Syria more $3.5 billion to buy oil, without which the country would have probably collapsed by now.