Anti-terrorism police and bomb disposal units have been called to a wooded area in West Dunbartonshire which is thought to have been damaged in an explosion.
Strathclyde Police were called to reports of an explosion in Garadhban Forest, near Gartocharn, at about 1200 GMT on Wednesday.
The area, to the south east of Loch Lomond, has been sealed off.
Police said enquiries were ongoing to establish the full circumstances surrounding the incident.
Speaking at a media conference Ch Supt Calum Murray, of Strathclyde Police, 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."
Ch Supt Murray said that several other agencies - including the Metropolitan Police - were involved in the investigation.
He said the investigation team was "not ruling anything in or out" at this stage, which he described as "the assessment phase".
Ch Supt Murray also said the damage in the woodland was "not an expansive area".
Officers are also collecting CCTV footage from local businesses within the general area of the explosion.
Hotel manager, Stuart King told the BBC: "I got a phone call last night from CID asking if I could meet them here as a matter of urgency and that they wanted to access our CCTV system.
He added: "I was here for four hours with two CID officers and the CCTV officers that work with Strathclyde Police."
Mr King said the officers gave him no details about why they were scrutinising the footage.
He said: "Today the police were coming in and out and staff were asking questions.
"We heard rumours that there had been an explosion and then saw it on the news website."
A Scottish government spokeswoman said: "Strathclyde Police are currently investigating this incident and are keeping ministers informed of their progress - they have reassured us that there is no threat to public safety."