Police officers continued to comb the area in Garadhban Forest at Gartocharn, near Loch Lomond yesterday following the explosion on Wednesday.
They refused to comment on reports that an explosive device had been found with a "unique blueprint", with some of the materials found to be "so unstable" they would need an "armoured vehicle" to remove them.
Terrorism experts said the length of the investigation suggested the incident was more than just youths experimenting with home-made explosives in the woods.
Strathclyde Police were called to the forest on Wednesday afternoon after a dog walker reported hearing an explosion.
Specialist officers and bomb disposal experts from the Metropolitan Police, the Royal Navy, Scotland Yard anti-terror officers and, it is believed, MI5 counter-terrorism agents were called in to examine the scene, which included several explosive devices and a tree that had been blown up.
Police insisted at the weekend they were following a number of "positive lines of inquiry", but refused to release further details.
Professor David Capitanchick, a terrorism expert from Robert Gordon University in Aberdeen, said police would need to be cautious about revealing too much information to ensure they could get a hold of whomever might be responsible.
He said: "The length of time and the number of authorities closing off the area suggests there's something serious. It's taken too long to reach the conclusion that this is nothing."
He added that terrorists could be "planning for something imminent". The investigation is centred around a woodland area about 300 yards from Ross Priory, a 19th century function venue owned by Strathclyde University.
In 2007, Glasgow Airport bombers Bilal Abdulla and Kafeel Ahmed spent several hours in the same remote woodland just before making their attack on the airport.
Today, the area remains cordoned off and police insisted there was no risk to anyone living, working or visiting the area.
Chief Superintendent Calum Murray, Divisional Commander, Argyll, Bute and West Dunbartonshire, said: "It is only right that we avoid speculating on the nature of this incident until we have considered and analysed any potential evidence."
Professor David Barclay, a forensic specialist, also at Robert Gordon University, said: "With these particular devices, the police will be trying to determine whether the design came from the internet or whether they were put together by a particular organisation. They are fortunate that some of the devices are intact as they will be able to scour them for DNA, which will help them to trace back where the components originated."