ANKARA (Reuters) - The leaders of Turkey and Russia marked the official start of work to build Turkey’s first nuclear power station on Tuesday, launching construction of the $20 billion Akkuyu plant in the southern province of Mersin.

The plant will be built by Russian state nuclear energy agency Rosatom and will be made up of four units each with a capacity of 1,200 megawatts.

Russian President Vladimir Putin and Turkey’s Tayyip Erdogan marked the start to construction, watching by video link from Ankara.

“When all four units go online, the plant will meet 10 percent of Turkey’s energy needs,” Erdogan said, adding that despite delays Turkey still planned to start generating power at the first unit in 2023.

Speaking at a later news conference with Putin, Erdogan said the cost of the project may exceed the planned $20 billion for the 4,800 megawatt (MW) plant, part of Erdogan’s “2023 vision” marking 100 years since the founding of modern Turkey and intended to reduce Turkey’s dependence on energy imports.

Since Russia was awarded the contract in 2010, the project has been beset by delays.

Last month, sources familiar with the matter said Akkuyu was likely to miss its 2023 target start-up date, but Rosatom, which is looking for local partners to take a 49 percent stake in the project, said it is committed to the timetable.

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The Interfax news agency cited the head of Rosatom saying the sale of the 49 percent stake was likely to be postponed from this year until 2019.

Turkish companies have been put off by the size of the financing required as well as by concerns they will not receive a sufficient share of the lucrative construction side of the deal, two industry sources have said.

Erdogan told the news conference Turkey may cooperate with Russia on defense projects besides the S-400 missile defense system which Moscow has agreed to supply to Ankara. He did not give further details.

Turkey signed an agreement to buy the S-400 system in late December in a move which raised concern in the West because it cannot be integrated into NATO’s military architecture.

Iranian President Hassan Rouhani will join Erdogan and Putin for a three-way summit on Syria in Ankara on Wednesday.