Iran rebukes Turkey on Syria incursion - Why?

Question

Turkey is in Syria launching an offensive against the Kurds, and Iran just issued a warning for Turkey to back off. This confuses me - isn't it in Iran's interest for Turkey to suppress the Kurds? Why would Iran issue the warning?

Here's my flawed understanding of geopolitics in that region:

Both Iran and Turkey are competing for middle-eastern influence, both having (unspoken) ambitions to become the head of a new Islamic caliphate - as a successor of the Ottoman empire, or at the very least, a USSR or European Union alliance of Middle Eastern nations.

So yea, I know they aren't buddies.

Syria is Iran's partner, but Turkey is basically helping Syria by fighting the Kurds. Kurdistan extends into Iraq, Turkey, Syria, and Iran, and all four of those nations don't want Kurdish independence. Turkey fighting Kurds helps Syria and Iran both, since it reduces the amount of resources either of them need to invest on the Kurds, freeing up Iran to continue it's proxy war against Saadi Arabia in , and to continue consolidating influence in Iraq.

It also frees up Syrian resources to focus on its ongoing civil war, and frees up Iran's Hezbollah proxy army which is getting ready to harrass Israel in a mini conflict - perhaps with Hamas, which is also prepping for another Israel skirmish.

Syrian and Turkish relations, as far as I can tell, have gone down and up, up and down, but they don't view each other as enemies, despite some serious disagreements and diplomatic incidents between the two (each as shot down airships from each other in the past decade, but they've also held military manuevers together). Turkey, while condemning Assad's "brutality" on the rebels, has maintained support for Assad and refuses to call for him to step down. So Turkey isn't buddy-buddy with Syria either, and there's some distrust of Turkey, but they aren't enemies (like Iran and Turkey are).

So why doesn't Iran want Turkey to fight the Kurds, if it frees up Iran & Co resources during a time when it seems likely they'll need those resources for other conflicts active and brewing?

A semi-related subquestion is:

Why did Syria previously support/shelter the Kurdish PKK group?

What am I failing to understand?

Answer 1

As you noted, there are now three players in the Syrian civil war: Assad forces, Syrian rebels (FSA, Ansar Al Cham, ...) and the Kurds. You seem to think that according to the "divide and conquer" principle, the two other players fighting would let Assad forces rest. The "divide and conquer" does not apply here.

Why doesn't Iran want Turkey to fight the Kurds ?

1. Syria only: Because it strengthens the opponents to Assad.

The Afrin offensive does not weaken the rebels at all. It gives them control over more land, and puts on Syrian soil a foreign army allied to them. This is mostly what worries Iran. From the public declaration of Rouhani:

a military foreign intervention should be based on the authorisation of the host country and its people

"host country and its people" meaning here the Assad government.

Also note that the Kurds are not equally dangerous to the Syrian government than the rebels, as they do not intend to control all the Syrian territory.

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Now outside of Syria, when you say something regarding syrian Kurds, the other Kurds pay attention.

2. Iranian Kurds: Because Rouhani wants to be "popular" among the iranian kurdish population

Recall that around 6 to 8 million Iranians are also Kurds. Rouhani and the reformist party have reached out to the Kurdish population of Iran for internal politics reasons. A public condemnation of the turkish operation is also an easy way to try to get more popularity.

Also note that there is an independentist kurdish movement in Iran. This could bring Iran closer to the Turkish position on overall Kurds, as shown by this state visit. But so far, Iran's separatists are far from being as active as Turkey's separatists, the PKK. There have been recent clashes, but not to the same extent. Which can explain why the iranian approach is different than Erdogan's.

3. Iraki Kurds: Because Rouhani also wants to improve the ties between iraki Kurds and the iraki government, another ally.

The iraki kurdistan is already quite autonomous from the bagdad government, and it could get even more so after the recent referendum. He does not want to weaken Irak with a full autonomy of the Kurdistan. Rouhani also publicly said he wanted to improve ties with the iraki kurdistan. Which gives him another reason to be Kurdish-friendly (as long as they are not separatists of course).