Ankara - Ukraine's ambassador on Thursday requested Turkey to close the Bosphorus and Dardanelles straits to Russian ships, after Russia launched.

Under the international Montreux Convention, NATO member Turkey has control over passage of vessels between the Mediterranean and Black Sea, making it a potentially key player in any military conflict between Russia and Ukraine.

The pact grants supervisory powers to Turkey, which neighbours Russia, Ukraine, Romania, Bulgaria and Georgia on the Black Sea:

The Montreux Convention Regarding the Regime of the Straits of 1936
The purpose of the convention was stated as regulating the passage and the transportation of vessels through the straits, in the context of the security of Turkey and the coastal states of the Black Sea. Under the 1936 accord, Turkey has control over the Bosphorus and Dardanelles and the power to regulate transit of naval warships. It also guarantees the free passage of civilian vessels in peacetime and restricts the passage of ships not belonging to Black Sea countries.

The Montreux Convention of 1936 was ratified by Turkey, Great Britain, France, the then USSR, Bulgaria, Greece, Germany, Yugoslavia, and Japan (with reservations).

In wartime, or when it is endangered by aggression, Turkey is sanctioned to close the straits to all foreign warships. It can also refuse transit for merchant ships from countries at war with Turkey and to reinforce the straits in case of a war.

All non-Black Sea countries sending vessels must notify Turkey 15 days in advance, while Black Sea nations must give eight days notification.

Passage is limited to nine warships of a specific aggregate tonnage at any one time, with no ship above 10,000 tonnes allowed to pass. A non-Black Sea country's ships cannot exceed a total 30,000 tonnes at any time, and the vessels are allowed to stay in the region no more than 21 days. Black Sea states may transit ships of any tonnage reported reuters.

Submarines can be send by Black Sea countries, through the straits with prior notice, as long as they have been built, purchased or sent for repair outside the Black Sea.

Civil aircraft are allowed to transit along routes sanctioned by the Turkish government. The accord does not specify restrictions on the passage of aircraft carriers, which Turkey claims to have control over as well.

President Tayyip Erdogan has said Turkey will do what is necessary as a NATO ally if Russia invades, without elaborating. Turkey which is reliant on Russia for energy and tourism would try to manage the crisis without abandoning ties with either Ukraine or Russia.

In 2008, when Russia recognised the independence of the two Georgian regions of Abkhazia and South Ossetia, Ankara rejected U.S. requests to let its warships pass the straits at a time when it depended on Russia for commodities and trade.

During World War Two, the Montreux accord prevented the Axis powers from sending naval forces through the Straits to attack the Soviet Union.
-Reuters