Why is Iran arming Serbia?
That has not happened.
Israeli support in the war (and I'm not talking about equipment) is vital
you can see how quickly they can smear you with genocide accusations and turn you into a pariah state.
Baku could have relied on Iran, Turkish support would have been sufficient as well. Instead they chose to turn to the zionists and cooperate with them against Iran.
The crux of the issue is that Aliyev is buying into the promise zionists have been whispering into his ear, that he could annex Azari-speaking provinces of Iran. There's some megalomania at play with this person, and that's dangerous, mostly for Baku itself.
Well, he's an ethnic Azerbaijani from Tebriz area so it's not surprising.
Supreme Leader Khamenei's policy choices are not informed by "ethno"-linguistic considerations at all.
But Iran as a state policy clearly doesn't support Azerbaijan like Turkey supports Azerbaijan. Or even to the degree that Israel supports Azerbaijan. Placing economic sanctions on Armenia would give Iran some leverage. Closing the Armenia border instead of threatening to defend it (lol) would make Iran suddenly much more valuable.
It's not like Armenia has any importance to Iran. Armenian lobby clearly doesn't support Iran.
All because of Baku's tilt towards Tel Aviv and their questioning of Iranian territorial integrity in line with the zionist master plan.
Despite the above Iran refrained from supporting Karabakh Armenians, and has to date stopped short of arming Armenia.
Why would an Islamic Republic help Armenia against Azerbaijan which is a Muslim country?
For now Iran has never extended military support to Armenia. This may change if the Baku republic decides to invade sovereign Armenian land (not Karabakh which legally is Azarbazijani territory, but the Zangezur corridor bordering Iran which belongs to Armenia).
Reason's quite straightforward and self-explanatory. Namely the fact that despite Iranian assistance to Azarbaijan during the first Karabakh war (Iran actually gave martyrs for Karabakh), the regime in Baku has kept eyeing Iran's Azari-speaking provinces and is entertaining the insane dream of annexing these, spurred on as it is by none other than the zionists with whom it entered a strategic alliance. Zionists who for their part are known to be seeking to balkanize Iran along "ethno"-linguistic lines.
Iran was the first country to recognize the Baku republic's independence from the Soviet Union. Also Iran gifted 500 million USD to Baku in the 1990's when the newly independent republic was facing serious economic issues, even though the Iranian economy itself was still recoverin from the immediate consequences of eight years of imposed war with Iraq (1980-1988). What's more, all these years Iran has been auhorizing Baku to use a land-based corridor through Iranian soil, allowing the Azarbaijan Republic to link up with its enclave of Nakhjavan located between Iran, Armenia and Turkey - again completely free of charge. Contrast this with how the Republic of Azarbaijan has recently gone over to heavily taxing and harassing Iranian truck drivers who pass through territory under its control.
In sum, Baku responded to Iran's forthcoming policy by operating a rapprochement with Isra"el". Other missteps included the assassination under dubious circumstances of an influential officer of the Azarbaijani military who was holding favorable views of Iran, arrests and imprisonment of other pro-Iranian Azarbaijanis including Moslem scholars, laws banning Islamic hejab, restrictive measures against Shia Moslem mourners during Ashura, repression of the local Talesh minority (the Talesh are speakers of an Iranian language).
This is despite the fact that what's now called Republic of Azarbaijan used to be part of Iran for several millennia, until the Russian empire invaded that land and separated it from Iran in the early 19th century i.e. not too long ago. Today assorted politicians in Baku can be seen attempting to incite "ethno"-separatism amongst Azari Iranians.
Brenda Schaffer, an Isra"el"i scholar focused on promoting Azari separatism, is officially holding meetings with and advising the Baku regime. She moreover conducted a photo session with an American CIA person on the Azarbaijani side of the border with Iran.
What's more, Iranian intelligence found that one or several of the assassins who murdered Iranian nuclear scientists at the behest of Mossad, was or were handled out the Republic of Azarbaijan. Likewise, an Isra"el"i spy drone shot down by Iran is said to have taken off from across the Aras. In line with this, an Isra"el"i television channel recently aired a program which suggested that Mossad spies responsible for sabotage operations against Iran's peaceful nuclear program infiltrated Iran via the Republic of Azarbaijan as well.
Not to mention how authorities in Baku stationed Syrian fighters hostile to Iran along the border. Recent reports suggest they may be joined by the MKO in future, an exiled terrorist cult and one of the most extremist opponents of the Islamic Republic (the MKO has a record of murdering over 10.000 Iranian citizens in the 1980's and joining hands with Saddam's Iraq against their own country during the war).
The people of Azarbaijan are mostly Shia Moslems but the regime ruling over them is a highly secularist one, which has no issues collaborating with Tel Aviv against Islamic Iran's national security and territorial integrity. It's a regime whose president will lay flowers at the feet of an eminently masonic symbol such as the obelisk.
https://www.aa.com.tr/en/asia-pacif...-decision-to-open-embassy-in-tel-aviv/2858393
This is inevitably bound to provoke tensions with Iran. Iran cannot be faulted for acting against this plot, can she. And in effect Iran has displayed vast amounts of restraint and strategic patience in order to avoid stepping into traps prepared by the zionists. After copious provocations directed at Iran, a red line has recently been drawn by the Supreme Leader. Namely, any attempt by Baku to bring about forceful change to legally recognized boundaries. In that case Iran will respond, either directly or indirectly due to the heightened threat it would represent to her national security. It could take the shape of support to Armenia but Iran could as well choose to mobilize other types of assets. There are various options at Iran's disposal.
Should Baku refrain from such an ill-conceived move however, then Iran in all probability will pursue diplomatic efforts to make the Aliyev regime realize the deep errancy of its current policy towards Iran.