Iran's semi-official ILNA news agency has reported that Turkmenistan border guards opened fire, killing two Iranian fishermen and detaining another two for trespassing.

Wednesday's report says the incident happened on Tuesday night when the four young fishermen were sailing near the edge of Iranian territorial waters in the Caspian Sea.

The report did not identify the fishermen but said they ignored frequent warnings by Iranian authorities to observe the borderline.

Incidents of Turkmen border guards opening fire and shooting at Iranian boats have been frequent over the past years. Fishing boats in the area 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.