Police investigating a mysterious explosion in the Scottish countryside have said they are following a number of "positive lines of inquiry".
Strathclyde Police have cordoned off woodland at Garadhban Forest at Gartocharn, near Loch Lomond, following the blast on Wednesday.
A fingertip search of the site has already been conducted.
Specialist officers, including bomb disposal trained officers, remain at the scene.
Ch Supt Calum Murray said the "painstaking" investigation would take some time.
He said: "The location of this explosion poses a significant challenge in terms of the size of the area and the terrain we are searching.
"This is a meticulous and painstaking operation which is understandably taking some time.
"It is only right that we carry out the most thorough of investigations and avoid speculating on the nature of this incident until we have thoroughly considered and analysed any potential evidence we may find.
"Police are following a number of positive lines of inquiry into the circumstances surrounding the explosion on Wednesday afternoon."
The investigation is centred around a wooded area about 300 to 400 yards from Ross Priory, a 19th century function venue owned by Strathclyde University.
The area remains cordoned off and police insisted there was no risk to anyone living, working or visiting the area.