Sweden submarine hunt - in 60 seconds

Swedish naval vessels are continuing to scour a stretch of water near the capital Stockholm, amid suspicions that a Russian submarine may be lurking there.

The Swedish military says it could use force against a foreign military vessel if one is found. Russia denies involvement.

Tensions between Russia and many of its European neighbours are high following this year's conflict in Ukraine.

BBC News attempts to unravel the mystery - in 60 seconds.

Video produced by Michael Hirst