Pact gives Turkey oversight of warship transit to Russia, Ukraine

Ukraine has asked Turkey to close the Bosphorus and Dardanelles straits to Russian ships, Ukraine's ambassador to Ankara said on Thursday, after Russia launched air and ground assaults on its neighbour.

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.

Earlier this month, six Russian warships and a submarine transited Turkey's Dardanelles and Bosphorus straits to the Black Sea for what Moscow called naval drills near Ukraine waters.

Here are details of the pact and supervisory powers it grants to Turkey, which neighbours Russia, Ukraine, Romania, Bulgaria and Georgia on the Black Sea:

TURKEY'S POWERS

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.

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

All non-Black Sea countries wishing to send 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.

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

Civil aircraft can be transited along routes authorised by the Turkish government. The accord does not contain restrictions on the passage of aircraft carriers, but Ankara says it has control over that as well.

TURKEY'S OPTIONS

Since tensions flared over Ukraine, Turkish officials have said only that Montreux is instrumental in keeping regional peace. President Tayyip Erdogan has said Turkey will do what is necessary as a NATO ally if Russia invades, without elaborating.

Turkey is reliant on Russia for energy and tourism, and has forged close cooperation with Moscow on energy and defence in recent years. It has also sold drones to Ukraine and called the Russian moves against Ukraine unacceptable. 

Erdogan said Turkey 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.