NICOSIA, Cyprus (AP) — ExxonMobil and partner Qatar Energy expanded their stake in potential oil and gas deposits off Cyprus by signing a deal with the east Mediterranean island nation Friday for a second exploration license in waters that Turkey partly claims.

Drilling off Cyprus has been a source of tension with neighboring Turkey since 2011, when Texas-based Noble Energy discovered the first natural gas off the ethnically divided island’s southern coast.

Cyprus Energy Minister Natasa Pilides said with the new license, ExxonMobil is expected to start exploration in the first half of next year to get a better estimate of potential amounts of oil and gas.

She added there are “sufficiently hopeful indications” that the geological makeup of the underwater area mirrors that of a nearby spot where ExxonMobil discovered in 2019 a sizable deposit estimated to contain 5-8 trillion cubic feet of gas. The two energy companies are drilling an appraisal well at that deposit to confirm how much gas it holds.

Varnavas Theodossiou, ExxonMobil Cyprus managing director, said the new license “enables us to further expand our presence in Cyprus in what we believe to be a promising region for offshore exploration.”

The development comes amid Turkey’s warnings that it would “never allow” anyone to carry out an “unauthorized” gas search in waters it claims partly fall under its control.

Cyprus’ ethnic split occurred in 1974 when Turkey invaded following a coup aimed at a union with Greece. Turkey doesn’t recognize Cypriot statehood but instead recognizes a Turkish Cypriot declaration of independence in the island’s northern third — the only country to do so.

Ankara insists Cyprus’ internationally recognized government seated in the south is “acting unilaterally” in exploiting offshore gas reserves and ignores the rights of Turkey and the breakaway Turkish Cypriots to the region’s hydrocarbon potential.

To drive the point home, Turkey has dispatched numerous warship-escorted drill and survey ships to carry out exploratory drilling inside Cyprus’ exclusive economic zone. It also claims some 40% of that zone either lies inside its continental shelf or belongs to Turkish Cypriots.

The Cypriot government says Turkey’s claims aren’t recognized by international law.

Cyprus also has licensed seven of its 13 offshore drilling areas to a consortium made up of France’s TotalEnergies and Italy’s Eni, which is expected to resume its own drilling in the first half of next year after a nearly two-year delay brought on by the coronavirus pandemic.

Pilides, Cyprus’ energy minister, said ExxonMobil and Qatar Petroleum aren’t “troubled” by Turkey’s threats and the deal is proof of that. She said the Cypriot government would carry on with its drilling program in line with international law.