Russia is continuing to build up its naval presence in the Black Sea, and The Sunday Times newspaper, quoting British naval sources, said Britain is also deploying two warships to beef up NATO’s presence, as tensions over Ukraine escalate.

Access to the Black Sea is through Turkey’s Bosphorus and Dardanelles waterways which are controlled by the 1936 Montreux Convention.

Retired Turkish Ambassador Mithat Rende, a maritime law analyst, said the current tensions underlines the treaty’s importance.

“Maritime powers, which are not are riparian states, they have limited access to the Black Sea," Rende said. "Because of the limited tonnage that each country cannot keep more than thirty thousand of tonnage capacity in the Black Sea and for a period for only 21 days. So, it probably desirable for certain countries, like the United States to have an alternative to Montreux."

Earlier this month, news reports said Russian President Vladimir Putin pressed his Turkish counterpart Recep Tayyip Erdogan to ensure NATO fully comply with the Montreux convention.

Huseyin Bagci of the Foreign Policy Institute in Ankara said Moscow sees the convention as key to Russian Black Sea hegemony.

“This is (the) only way which makes Black Sea at the same time a Russian sea, because the Russian navy is there dominating," Bagci said. "And the American warships are limited there. And so, it's good for Russia to have Montreux, maybe more than Turkey.”