The 1936 Montreux Convention allows Türkiye to cut off any vessel transit between the Black Sea and the Mediterranean during wartime.
Shortly after Russia launched air and ground assaults against Ukraine on Thursday morning, Kiev made an official request to Ankara to close the Turkish straits to Russian ships.
“We are calling for the airspace, Bosphorus [Istanbul] and Dardanelles [Canakkale] Straits to be closed. We have conveyed our relevant demand to the Turkish side. At the same time, we want sanctions imposed on the Russian side,” Ukrainian Ambassador to Türkiye Vasyl Bodnar said in a presser in Ankara.
Türkiye said it does not want further escalation and called on Russia to halt all actions in Ukraine.
Türkiye “has studied all possible scenarios regarding Montreux Convention. All the legal and diplomatic preparations have been done. We will continue to follow the developments,” governing AK Party’s spokesman Omer Celik said.
Ankara is observing the possible economic, political and related impacts of ongoing Russian aggression on Ukraine, he said.
The request puts Türkiye, a NATO member which shares a maritime border with Russia and Ukraine in the Black Sea, in a unique bind. It has good ties with both countries and has positioned itself as a neutral mediator for peaceful resolution to the crisis, making it an essential player in the current conflict.
Under the 1936 Montreux Convention, Ankara has control over the straits and can limit any vessel – civilian or military – from transit during wartime or if threatened.
Here’s more on the convention:
Before the Montreux Convention, the Turkish straits were regulated by the 1923 Lausanne Convention, which had established some rules about how military ships could use the straits.
In 1933 Adolf Hitler came to power in Germany and vowed to follow expansionist policies.
In 1936, Britain, the Soviet Union and Türkiye met in Montreux, Switzerland, and agreed to return the straits (the Bosphorus, the Dardanelles and the Sea of Marmara) to Turkish control.
The Montreux Convention was ratified by Türkiye, Britain, France, the USSR, Bulgaria, Greece, Germany, Yugoslavia and Japan.
The three most important positions that needed to be balanced were between Türkiye, the USSR and the UK. Türkiye wanted to remilitarise the area and gain as much control over the straits as possible; the USSR wanted unrestricted passage so their Black Sea fleet could have access to the Mediterranean; and the British wanted some limitations placed on the USSR’s influence in the Mediterranean.
The accord ended up being a compromise between those three considerations.
What are the rules?
The accord guarantees free passage of civilian vessels to use the Turkish straits, unless they are from a country that Türkiye is engaged in war with, giving it the authority to close the straits to all merchant ships if it chooses.
With warships, there are more restrictions. If Türkiye is at war, Ankara has the right to do whatever is necessary, including closing the straits. If other states are at war and Türkiye is neutral, the straits are closed for those belligerent countries.
In peacetime, the rules are a bit more complicated.
The convention does not allow aircraft carriers, but it does not mention ships that are designed for other purposes but can also carry aircraft. In this case, Ankara is the ultimate decision maker depending on war and peace time.
The Turkish government must also authorise aircraft if they cross over the straits.
Submarines are also not allowed to pass the Turkish straits. But Black Sea states – Russia, Ukraine, Bulgaria, Romania and Georgia – can build submarines outside the Black Sea and transport them through the straits, and can exit the Black Sea for maintenance by providing adequate notice.
Türkiye's Foreign Minister Cavusoglu underlined that experts are working on determining whether there is a belligerency.
If Ankara decides it is a war, it can ban vessels, Cavusoglu added, noting that Türkiye is not a part of any war.
"But even if we ban it, Russians have right [of passage]. During negotiations, Russia has had amended that clause. Articles of 19, 20 and 21 are regulating them," he said.
There is also limited naval presence provided for non-Black Sea states. For example, they cannot pursue expedition operations, nor have a ship pass that is larger than 10,000 tonnes. A non-Black Sea country’s ships cannot exceed a total of 30,000 tonnes at any time, and are allowed to stay in the region for no more than 21 days.
The Black Sea states' war vessels that are larger than 15,000 tonnes can pass the Straits singly, escorted by not more than two destroyers with prior adequate notice.
All non-Black Sea countries wishing to send vessels must give 15 days notice to Ankara for passage, while Black Sea states have to give a notice of 8 days.
The 1994 UN Convention on the Law of the Sea has prompted calls for a revision of the Montreux Convention. However, Türkiye is not a signatory to the UN treaty due to its longstanding dispute with Greece, so the Montreux pact has remained in place.
Since tensions have flared over Ukraine, Turkish officials have maintained that Montreux is instrumental for preserving peace in the region.
There has been no specification of what position Türkiye would take if war between Russia and Ukraine broke out.
So far, President Recep Tayyip Erdogan has said Türkiye will act in unity with its NATO allies if Russia invades.
On Tuesday, Erdogan called Russian President Vladimir Putin’s recognition of Ukraine’s separatist regions “unacceptable” and a clear violation of Ukraine’s sovereignty.
In the aftermath of today’s Russian attack on Ukraine, the Turkish President tweeted that “Türkiye supports Ukraine’s struggle to protect its territorial integrity” and he “regretted” that the two sides Ankara has close ties with had “come face to face in this way.”