Azerbaijan accused Turkmenistan of starting exploration at the disputed Kapaz (Serdar) deposit in the Caspian Sea and said it would take “appropriate measures” if the Central Asian nation didn’t stop.

Turkmenistan’s Foreign Ministry said on June 19 it was officially protesting what it called “illegal measures” by Azerbaijani border guards against a Turkmen vessel that was carrying out “research” in the disputed zone. The statement accused Azerbaijan of “provocations” but gave no further details. Earlier, Azerbaijan’s Foreign Ministry summoned the Turkmen ambassador to Baku to warn against what the ministry described as Turkmen attempts to explore the disputed zone.

Baku calls the oil field Kapaz, while Ashgabat calls it Serdar. Both sides claim ownership. Exploration at the field violates an agreement signed by the two countries in 2008. After this agreement any exploratory or extraction activities in the area is refrained until the dispute is resolved.

The rich field was discovered in 1959 by Azerbaijani geologists and geophysicists. In 1983 the area was prepared for deep exploratory drilling by Azerbaijani oil workers, which took place in 1986. After the disintegration of the former Soviet Union in 1991, the five littoral states, Russia, Iran, Azerbaijan, Kazakhstan and Turkmenistan, have failed to agree on the maritime boundaries of the Caspian Sea Baku has insisted on dividing the sea along a median line from the shore, giving it the lion’s share of oil reserves, while Turkmenistan wants the division to take into account where the oilfields lie relative to the shore.

While Turkmenistan and Azerbaijan are fraternal nations, years of mutual rivalry, misunderstanding, and enmity cast a shadow on their relations. Azerbaijan is more open to the West and closely cooperates with NATO and the EU, while Turkmenistan maintains close ties to Russia. Many expected that the proposed Nabucco pipeline, designed to connect Caspian gas fields to Europe through Turkey, would provide a natural point of alliance and cooperation for Turkmenistan and Azerbaijan. However, differences between the countries persist, especially with regard to Nabucco’s reputation as an “anti-Russian” project.