Ukraine accused Russia at an international court on Monday of flouting sea law by trying to keep the Kerch Strait between mainland Russia and annexed Crimea under its sole control.

The €3.15-billion, 19-kilometre bridge built by Russia across the Kerch Strait after it annexed Crimea in 2014 is meant to enable the Kremlin to control Ukraine's Sea of Azov, Kyiv's legal representatives said in front of the Permanent Court of Arbitration.

The Supreme Court in Ukraine's Russian-occupied Crimea region said on September 23 that it sentenced a Ukrainian citizen identified as M. Seleznov to 14 years in prison for espionage.

"Our support for Ukraine's territorial integrity, sovereignty and independence is unwavering," the Turkish president said.

Ukraine has accused Russia of seeking to illegally seize control of the strategically important Sea of Azov and Kerch Strait