Turkey has agreed “in principle” to allow the South Stream gas pipeline to pass through its territorial waters, Yury Ushakov, deputy head of the government staff, said Wednesday, ahead of a visit by Prime Minister Vladimir Putin to Turkey.

Putin’s trip follows a signing ceremony in Ankara last month for transit agreements for the rival Nabucco gas pipeline, a European Union-backed project designed to counter Russia’s strong influence on European energy supplies.

“An agreement has been reached in principle to start construction work,” Yury Ushakov, deputy head of government staff, told a news briefing. He said the Turkish government will also give permission to begin a feasibility study “within days.”

A Turkish government source who declined to be identified confirmed that Turkey will agree to allow the South Stream gas pipeline to pass through its territorial waters.

Ushakov said a protocol on cooperation in the gas industry, due to be signed by Putin and Turkish Prime Minister Tayyip Erdogan on Thursday in Ankara, would also set a date for the start of construction work.

Russia, which supplies a quarter of Europe’s natural gas, wants to accelerate construction of gas supply routes to bypass Ukraine and other ex-Soviet states after arguing with Kiev over transit payments several times in recent years.

The agreement would mark a new victory for Russia in its fight to undermine the construction of the Nabucco pipeline. Had Turkey rejected the South Stream project, Russia would have been forced to go through Ukraine’s territorial waters.

Ushakov said the agreement does not mention any gas marketing rights for Turkey — a thorny issue in Turkey’s previous negotiations with Russia over gas transit to Europe, as well as in talks on the Nabucco project.

Ushakov said Putin and Erdogan have developed “a personal chemistry” that helps them deal with “the most difficult issues.”

Ankara is also looking for Russian oil that would fill up a planned government-backed oil pipeline that is expected to travel from the Black Sea coastal town of Samsun to the Mediterranean oil hub of Ceyhan.

Ushakov said the two sides will “express readiness to start a realization” of the project and agree to create a working group. He said Russia made some concessions on the oil pipeline issue in exchange for Turkish concessions on South Stream. “We made a compromise of sorts,” he said.

“They made concessions on South Stream. We made some concessions on the Samsun-Ceyhan pipeline. The concessions are that we need to carefully study this project.”