In a rare, strongly worded tweet on Friday, Iran’s Foreign Minister Mohammad Javad Zarif slammed Turkish President Recep Tayyip Erdogan for a speech on Thursday which many Iranians have interpreted as an irredentist provocation regarding Iranian territory and Turkey's ally the Republic of Azerbaijan.

Later on Friday, Iran's foreign ministry summoned the Turkish ambassador and demanded an explanation for Erdogan's action.

During a visit to Baku Thursday to celebrate the country's recent victory in the Nagorno-Karabakh conflict, Erdogan recited a folk poem, popular both in the Republic of Azerbaijan and the Iranian provinces of Azarbaijan that laments the division of Azari speakers by the river Aras which separates Azerbaijan and Armenia from Iran.

In the same speech in the pompous victory parade Erdogan called Turkey and Azerbaijan "one nation, two states" with reference to their shared linguistic heritage.

"One nation" could also be a possible reference to an empire of speakers of Turkic languages such as the language spoken in Iranian Azari populated northwestern region and the Republic of Azerbaijani.

"Those [who advised] Erdogan had not told him that the poem that he mistakenly recited in Baku is about the forcible separation of the regions to the north of Aras river from their motherland Iran," Zarif retorted in his tweet.

By mentioning "the motherland" he was referring to the cessation of the ancient Iranian territories to the north of Aras to Tsarist Russia in the 19th century by the kings of the Qajar dynasty. These consisted of large parts of today's Republics of Azerbaijan, Georgia and Armenia. Many Iranians are still very bitter about the loss of these territories to Russia.

"Didn't he know that he has spoken against the sovereignty of the Republic of Azerbaijan," Zarif asked sarcastically implying that the song meant annexation of the Republic of Azerbaijan to Iran -- if the historical separation was to be reversed -- not the other way around. "No one can talk [like that] about our dear Azarbaijan," he warned.

While the ancient name of the region was Azarbaijan – not Azerbaijan – the northern Soviet part assumed the new spelling in the 20th century.

Separatist pan-Turkism has been on the rise among Azari (Torki) speakers of Iran, particularly in the past two decades. Separatist groups, who call Iran’s northwestern regions ‘South Azerbaijan,’ launched strong media and social media campaigns in support of the Republic of Azerbaijan as soon as the fighting broke out in late September. According to human rights organizations, Iranian security forces have arrested several activists supporting the movement in the aftermath of the conflict.  

The language spoken in Iran's East and West Azarbaijan and several other regions and the Republic of Azerbaijan is also a Turkic language which dates back to the migration of Turkic tribes to the region in the 11th century AD. The language which is unrelated to Persian, but borrows a lot of words, is the driving force of a pan-Turkic movement in northwest Iran which advocates unification of its speakers on the two sides of the Aras river.

According to the CIA World Factbook, 16 percent of the Iranian population speak Azari Turkish with an additional 2 percent who speak other Turkic languages such as Turkmen and Qashqai. Azari is the predominant first language in the provinces of East and West Azerbaijan, Ardabil and Zanjan – an area that is also home to Kurds, Persians and other groups and where Farsi is the lingua franca as in the rest of Iran.

The name Azerbaijan was adopted in 1918 to refer to the territories, historically known as Caucasian Albania, which make up today's Republic of Azerbaijan after the collapse of the Russian Empire.

Azarbaijan evolved for the region’s ancient name which in old Persian meant "The land of the [Holy] Fire" and was used to refer to the territories in the south of the Aras river. The region now forms the three provinces of East and West Azarbaijan, as well as Ardabil and some of their surrounding areas.