An explosion in a remote forest area is being investigated by counter-terrorism officers.
A member of the public reported the explosion in the Garadhban forest in Gartocharn near Loch Lomond on Wednesday.
Police said there was damage to trees and that they suspected explosives had been involved. UK-wide agencies including the Metropolitan Police, the Royal Navy and the Ministry of Defence, are helping local police assess the scene.
It is not yet known whether the incident is linked to terrorism.
Chief Supt Calum Murray, Divisional Commander, Argyll, Bute and West Dunbartonshire, said: "As you would expect, when we are dealing with a situation where we suspect that explosives may be involved, it is our immediate priority to assess the situation and to call on expertise where we think it is appropriate.
"By its very nature, this type of assessment and investigation is complex and does take time. I can confirm that we are currently being assisted by agencies from across the UK. I would stress that the site is secure and that there is no risk to public safety."