"Holding quadrilateral sessions under official, non-official, or consultations topics, in the absence of one, or more countries, not only leads to dissatisfaction, but would pave the way for the emergence of irremunerable misunderstandings, opening the way for the emergence of unilateral solutions," Mottaki said.
The Presidents of Azerbaijan, Kazakhstan, Turkmenistan and Russia met in the western Kazakh city of Aktau on Thursday to discuss 'sub-regional cooperation.
In the letter, the Iranian top diplomat also expressed hope that the wisdom of Kyrgyz leaders would block the path for holding any further session in the absence of one, or more members, when the votes of the entire littoral countries are needed at the bottom of any document.
Meantime, an official at Kazakhstan's foreign ministry on Wednesday alleged that issues related to the legal regime of the Caspian Sea would not be discussed at the Thursday summit.
"In the unofficial summit of the four regional countries in Aktau the issues related to the legal regime of the Caspian Sea and the division of the Sea bed will not be negotiated," Yerjan Asheqbiov told reporters just a day prior to the summit.