The Turkish navy intercepted a marine drone in the Black Sea off Istanbul, authorities said, with media reporting that it contained explosives and might be Ukrainian.

Since the start of Russia's invasion of Ukraine in February 2022, a number of mines suspected of having floated down from the conflict zone have been spotted off the Turkish coast.

Measuring three metres (10 feet) long by one metre wide, the unmanned craft, "believed to have come from the northern Black Sea, was secured by teams from the Turkish navy", the Istanbul police authority said in a statement.

The public prosecutor's office has opened an investigation.

Turkish television news channel NTV reported that the unmanned craft contained explosives, which it said could belong to Ukraine.

Turkish authorities did not confirm the presence of explosives or the drone's origins.

But a yellow-and-green emblem believed to be that of the Ukrainian petrol station chain OKKO was clearly visible on the front of the craft.

The company is popular within the Ukrainian military because of its donations to the armed forces.

In January, NATO members Turkey, Bulgaria and Romania signed an agreement on demining the Black Sea during Russia's war in Ukraine.

Since Russia's invasion of Ukraine, both sides in the conflict have planted sea mines to protect their coastlines.

Some mines have washed up in the waters of the three NATO countries, endangering shipping and complicating Ukraine's efforts to break through a Russian naval blockade.

At the end of December, a Panama-flagged cargo ship heading for a Ukrainian port to load grain hit a Russian mine in the Black Sea.

Two sailors were injured in the incident, Ukrainian authorities said.