On the sidelines of the energy gathering, Turkish President Tayyip Erdogan has met his Russian counterpart Vladimir Putin in Istanbul. They spoke on energy deals, trade and tourism ties, defence, and the conflict in Syria -- of which the leaders back opposing sides. Earlier, both leaders had agreed to fully restore bilateral ties.

They are meeting for the third time since June, after Erdogan apologised for the downing of a Russian jet last November. But a Turkish foreign affairs advisor is not fully positive towards the warming relations, saying Russia and Turkey are not on the same page when it comes to Syria.

"There is no expectation on full compromise on the Syrian issue. Because there are some major differences for that, for the future of Assad, moderate opposition elements, so there is no common ground for the two countries to have some agreements on that," Professor Selcuk Colakoglu with Center for Strategic Research , Turkish Ministry of Foreign Affairs, said.