The government of Turkmenistan said it was taking an offshore oil dispute with Azerbaijan to an international court of arbitration.
In mid-June, the foreign ministry in Turkmenistan accused the government of Azerbaijan of illegal actions at a disputed offshore field in the Caspian Sea.
The field, called Kapaz on the Azeri side and Serdar in Turkmenistan, holds an estimated 580 million barrels of oil and 1.1 trillion cubic feet of natural gas.
Turkmenistan's acting Minister of Oil and Gas Kakageldi Abdyllayev said his government has "repeatedly" called on Baku to stop working in the area because authority hasn't yet been defined, the regional Trend news agency reports, citing state media.
Turkmenistan and Azerbaijan haven't agreed on maritime borders since gaining independence from the Soviet Union in 1991.
"In this situation, Turkmenistan has no choice, but to turn to the U.N. International Court," he said.
Abdyllayev said the field is "entirely" within Turkmenistan's territorial boundary in the Caspian Sea.
Iran last week announced it made an oil discovery off its northern coast in the Caspian Sea. The field could be situated in Azeri waters, however.