Tensions at sea between Russia and Ukraine

The commander of Ukraine's navy has told the BBC that his country has not lost control of the the strategically important Sea of Azov - saying there would not be a repeat of what happened four years ago in Crimea.

The Sea of Azov borders the conflict area in eastern Ukraine and in 2003 Russia and Ukraine agreed to give each other's ships free movement throughout its waters.

In recent months Russia has increased its military presence and inspections, with some calling its actions an "economic blockade" of Ukraine's Azov ports.

Jonah Fisher reports.