Russia on Thursday relocated three warplanes equipped with hypersonic missiles to its exclave of Kaliningrad on the coast of the Baltic Sea. 

On Thursday, "three Mig-31i aircraft with Kinzhal hypersonic missiles were relocated to the Chkalovsk airfield in the Kaliningrad region," Russia's Defense Ministry said in a statement. 

It said that they will be on "Round-the-clock combat duty."

Russian President Vladimir Putin, who unveiled the Kinzhal missile in 2018, has termed it "an ideal weapon" that flies at 10 times the speed of sound, making it extremely difficult for missile defenses to intercept.

Russia in June clashed with Lithuania after Vilnius banned the rail transit of sanctioned goods from mainland Russia to Kaliningrad. 

The EU, however, said Lithuanian must allow Russian goods to transit with the exception of weapons. 

Seized by the Red Army from Germany in the closing stages of World War II, Kaliningrad was separated from the Russian mainland following the break-up of the Soviet Union when Lithuania became an independent state.

Kaliningrad was until 1946 known as Königsberg, and was the capital of the German state of East Prussia.

The settlement of modern-day Kaliningrad was founded in 1255 on the site of the ancient Old Prussian settlement Twangste by the Teutonic Knights during the Northern Crusades, and was named Königsberg in honor of King Ottokar II of Bohemia.

A Baltic port city, it successively became the capital of the State of the Teutonic Order, the Duchy of Prussia (1525–1701) and East Prussia.

Königsberg remained the coronation city of the Prussian monarchy, though the capital was moved to Berlin in 1701.