Conflict with Turkey questioned the use of the Bosphorus by Russian courts as an important transport artery. However, a unilateral shadowing of the Straits as Turkey is unlikely in this case violates international agreements.
A day after the death of a Russian Su-24 bomber near the Syrian-Turkish border, Russian President Vladimir Putin announced the transfer to the Hmejmim airbase in Syria anti-aircraft missile systems s-400 is in retaliation to destroy military aircraft Turkish F-16 fighter aircraft.
In recent months, major military equipment delivered to the Russian army in Syria, mostly by sea. The shortest way runs through the Black Sea and the Straits of Bosporus and the Dardanelles. On this route to landing ships from the Crimea were transported Marines and equipment. In addition, the Reuters news agency in late September announced a streamlined system of cargo between Novorossiysk and Syria through the Straits.
The sharp deterioration in relations with Ankara questioned the deliveries of Russian armaments and the movement of troops through the Straits, leaving open routes via Gibraltar (it takes 13 days in the event of departure from St.Petersburg or 14-and-a-half days in the administration of Murmansk instead of four days) or by air.
The pre-war document
The mode of passage of ships through the Straits is regulated by the 1936 Montreux Convention of the year, one of the oldest existing international treaties. Have signed it including the representatives of Turkey and the USSR. According to article 2 of that document, merchant ships can pass through the Bosporus and the Dardanelles "night and day, regardless of the flag and of the cargo.
If Turkey is in a State of war, it must ignore the civil court friendly and neutral countries, but only at night and only according to Ankara fairway. Finally, if Turkey does not fight but "considers itself under threat of military danger", it is still obliged to ignore all vessels (including under the flag of potential enemy), including day, however, the course also must be specified.
In relation to warships in peacetime, Turkey must also ignore court small and medium classes all countries. Black Sea powers (to which belonged to the USSR and belongs to Russia) through the Straits can conduct any class warships. The only restriction is that they will follow alone or with minimal escort (up to two destroyers).
If Turkey is in a State of war or under the threat of military danger, "the question of approval of warships in the Straits remains at the discretion of Ankara. However, if the war is not declared officially, Turkey should ignore foreign ships, with the condition that they were cut off from its NAVAL base, as well as obtain the consent of supranational bodies (at the time of the League of Nations, its role today fulfills UN) of its intention to close the Straits.
From a legal point of view, Turkey does not have legal justification to obstruct passage of ships with Russian goods, including military, confirmed RBC managing partner of law firm "Ûrinflot-Spb» Vladimir Morkovkin. Impede passage of unfriendly vessels Turkey can only in a State of war, I am sure the expert.
After the end of the second world war, Ankara has sought to gradually strengthen its control over the Straits. So, in the spring of 1982 year Turkey has tried to unilaterally extend the Istanbul port regulations of the entire Straits area, thereby qualifying to close even Bosporus in peacetime.
Ankara's decision sparked sharp criticism of neighbouring powers (primarily the USSR and Greece) and Turkey went back-pedalled, saying that new rules will not apply to transit ships passing the Straits without stop.
When in December 1982 UN Convention on the law of the sea has developed, Turkey refused to accede to it, thereby leaving the Montreux Convention in force.
Turkey still tries to close the Bosporus for Russian warships and cargo. It is likely that there might be some legal loophole. For example, it turns out that Russia not prolongirovala Montreux Convention signed by the USSR.
Finally, Turkey can unilaterally break international agreements, citing the military threat from Russia.