An investigation is under way in Derry after a sonar scan revealed a submarine-shaped object buried in the bed of the River Foyle.

The discovery has sparked intense speculation that it might be a relic from World War Two.

Given Derry's significance during the war, the scan has sparked a multi-agency investigation and it is believed photographs of surrendered German U-boats lined up at Lisahally Port could hold the key.

The image was captured by Mallow Search and Rescue who are often called upon during search operations.

They use specialist sonar equipment that was donated by the Brian O'Tuama Fund in Cork.

The Mallow team hopes to learn more when they perform a second scan of the river bed in the coming days.