Security has been stepped up across Scotland exactly four weeks after the suicide bombings in London.
Armed response units are on stand-by for deployment
Armed response units were on standby for deployment to all major rail hubs, air and sea ports to prevent further terror attacks on British soil.
Extra resources were deployed around transport networks which have connections to London.
Police chiefs stressed security had been heightened as a precaution not because of any specific threat.
Peter Wilson, president of the Association of Chief Police Officers in Scotland, said: "We have additional uniformed patrols on duty at these areas in Scotland to complement the increased security presence in London.
"Armed response vehicles and patrols are available for deploying to all mainline railway stations, based on intelligence assessments. We are flat out."
'Spotters' at airports
The move comes two weeks on from the 21 July attempted attacks, which were themselves mounted exactly two weeks after the 7 July bombings.
Special Branch "spotters", intelligence specialists trained to detect suspects, were on duty at arrivals and departures areas in Scottish airports.
Vehicles and passengers coming into the country at ferry ports in Stranraer and Rosyth were also subject to increased scrutiny.
Mr Wilson, who is also chief constable of Fife Constabulary, said: "We continue to monitor all rail stations, air and sea ports for any persons of interest who may be travelling.
"The public have been tremendous, they are our eyes and ears and they recognise police forces across the UK are there to provide that reassurance."
Meanwhile, Scottish police joined colleagues from across the UK in London to help take the strain off the Metropolitan Police as it mounts one of the biggest security operations the capital has seen since World War II.
Officers from Scotland were on patrol at Charing Cross as part of the show of strength at rail and Tube stations, Detective Chief Constable Andy Trotter, of British Transport Police said.