We are strongly protesting the indiscreet action of Turkmenistan’s border guards in shooting at a fishing and civilian boat," Foreign Ministry spokesman Bahram Qassemi said in a statement on Thursday.
The incident reportedly happened on Tuesday night when the four fishermen were sailing near the edge of Iranian territorial waters in the Caspian Sea.
Qassemi said, "Immediately after the incident and the circulation of this unfortunate news, the Foreign Ministry and Embassy of the Islamic Republic of Iran in Turkmenistan contacted Turkmen authorities and seriously followed up the issue."
They filed an official note, asking Turkmenistan's government for an explanation about the incident, the spokesman said, stressing that further follow-ups were continuing.
"Even if the Iranian fishermen had approached Turkmenistan’s waters, based on the usual international practice, the border guards could have driven them away from the stretch of their country’s waters,” he said.
"Therefore, we call for an immediate and official explanation from the responsible authorities in Turkmenistan and hope that, given the friendly relations between the two countries, all aspects of the incident will be clarified with the cooperation of the country's competent authorities," Qassemi added.
In recent years, incidents of Turkmen border guards opening fire and shooting at Iranian boats have become frequent in the Caspian Sea where fishing boats often report poor visibility and technical failures.
Iran, Turkmenistan, Azerbaijan, Kazakhstan and Russia share the Caspian Sea, an inland sea that is a lucrative source of caviar, gas and oil.