Turkey is considering deploying a Russian missile-defense system along the country’s southern coast, near where its warships are accompanying vessels exploring for energy, according to four people with knowledge of the deliberations.

The long-range S-400 battery, which might be delivered in weeks, would dramatically enhance Turkey’s military capabilities in the Eastern Mediterranean, where it’s embroiled in a spat with European Union member Cyprus over offshore gas exploration, the people said on condition of anonymity as the issue is sensitive.

The Mediterranean is not the only location under consideration and other options are also being looked at, the people said. If approved, a southern deployment would send a strong message to Turkey’s rivals and allies that it’s determined to protect its security and economic interests, they added. Spokesmen for the Turkish government did not respond to calls for comment. Late Thursday, the country’s National Security Council said in a statement that: “Turkey will continue its activities in line with the international law and not allow faits accomplis in East Mediterranean.”

Turkish President Recep Tayyip Erdogan and President Donald Trump are expected to discuss the missiles on the sidelines of a G-20 summit in Japan next month.

The U.S. has threatened to sanction Ankara if it goes ahead with the missile deal, concerned that adding Russian hardware to NATO-member Turkey’s military could enable Moscow to gather critical military intelligence. It has also warned that Turkish ambitions to begin offshore drilling operations in an area claimed by Cyprus as its exclusive economic zone “risks raising tensions in the region”.

“Turkey regards the S-400s as a deterrent to defend its energy interests in the East Med where brewing tensions may threaten to bring Turkey’s relations with the U.S. to a breaking point,” said Mehmet Seyfettin Erol, head of Ankara-based research institute ANKASAM. “It feels increasingly threatened in the Mediterranean by U.S. and Israeli support for Cyprus.”

Defense Minister Hulusi Akar said last week that work was still underway to determine where the S-400s could be deployed. In April, Akar said that the S-400s might be used to defend the capital Ankara, the commercial hub of Istanbul, the southern Incirlik air base or an unidentified industrial facility. The unnamed location could be Turkey’s first nuclear power plant, being built by Russia in Akkuyu on the Mediterranean coast, the people said.

Russia hasn’t attached any conditions to where Turkey should deploy the missiles, said Igor Korotchenko, head of the Moscow-based Centre for the Analysis of World Arms Trade. “Turkey is a sovereign country. Erdogan can put them wherever he wants.”

Russian role

The S-400, also known within NATO as the SA-21 Growler, has advanced radars and is designed to defend airspace against warplanes used by countries in the western military alliance. Chief among U.S. concerns is that the Russian system could be used to collect data on the F-35 fighter jet’s stealth capabilities.

Turkey has refused to scrap its deal with Moscow and deploying S-400s on the Mediterranean could alarm other countries operating F-35s in the region, including the U.K. and Israel.

Installing the missiles in Turkey would mark a further advance in President Vladimir Putin’s efforts to engineer a bigger Russian role in the Middle East.

“The possibility of the S-400s being deployed at Akkuyu is quite strong,” said Abdullah Agar, a Turkish security analyst. “It is a solution that could provide security to the nuclear plant in line with Turkey’s cooperation with Russia and give it an edge in a stiff energy competition in the East Med.”

For some of Turkey’s military and civilian leadership, history is also an influence. They bitterly remember a crippling U.S. arms embargo imposed after Turkey invaded the northern third of Cyprus in the wake of an attempted coup to unite the island with Greece in 1974.

Significant quantities of natural gas have been discovered off the coasts of Egypt, Israel and Cyprus over the past decade, including by Exxon Mobil Corp., spurring hopes for a regional energy hub. Still, companies have struggled to overcome longstanding political and legal hurdles and find viable export markets, leaving investors questioning whether firms can realize the potential.

The internationally recognized government of the Republic of Cyprus has licensed several offshore blocks, some in disputed waters, drawing threats from Turkey which objects to Cypriot exploration without an agreement on sharing the proceeds of any finds. Turkey wants maritime boundaries in the area to be fixed to safeguard its rights, as well as those of the Turkish Cypriot state only Ankara recognizes.

“Turkey has the longest coastline in the eastern Mediterranean and it is expecting countries in the region and outside to respect its and Turkish Cypriots’ rights,” Akar told foreign military attaches aboard a Turkish frigate during a major naval exercise on May 25.