Turkish President Recep Tayyip Erdogan is meeting with his Russian counterpart Vladimir Putin in Istanbul.
The Wednesday's meeting is being held ahead of the launch ceremony of TurkStream natural gas pipeline project in the city, which the two leaders are set to attend.
Serbian President Aleksandar Vucic and Bulgarian Prime Minister Boyko Borisov are also expected to attend the ceremony.
Security measures are high in the city, as a total of 7,200 police officers are on duty for the inauguration ceremony.
Among security forces are 300 special operations teams, 30 bomb squad working around the hotels where foreign leaders are staying or on the routes they are traveling before and during the event.
Also, three police helicopters, four marine boats, four specially trained dogs and 30 armored vehicles are supporting the Turkish security forces.
Following the ceremony, Erdogan is later to host leaders of Russia, Serbia and Bulgaria in a dinner.
TurkStream natural gas pipeline project, which will carry natural gas from Russia to Europe via Turkey, is considered a further step in Turkish and Russian relations in terms of energy.
The TurkStream natural gas pipeline has a total capacity of 31.5 billion cubic meters, out of which the first line will carry 15.75 billion cubic meters of Russian gas to Turkish consumers.
The second line will carry another 15.75 billion cubic meters of gas to Europe via Turkey.
BOTAS built the first line that will connect to Turkey’s existing gas grid, while the second line, to be operated by a Gazprom-BOTAS joint venture, will stretch to the Turkish-European border in Turkey's Thrace region.