A major counter-terrorist exercise has begun in Edinburgh, simulating an attack involving firearms and a lorry hitting pedestrians.

The three-day Border Reiver exercise is designed to test responses of emergency services to a cross-border incident.

The Royal Bank of Scotland's headquarters at Gogarburn were used as one of the locations for the operation, which involved Police Scotland and Northumbria Police.

The scenario involved terrorists driving a lorry into a marquee full of people before getting out of the vehicle and shooting indiscriminately.

Actors played the role of casualties in the attack, lying on the ground and shouting for help.

The terrorists then entered a nearby building, with armed police forced to storm the premises.

Home secretary Amber Rudd will chair an Cabinet Office briefing room meeting (Cobra) as part of the scenario, with First Minister Nicola Sturgeon also involved.

Other police operations will take place at smaller locations in Scotland and the north of England in the coming days.

Police have said the exercise was not in response to any specific threat and was the result of a year of planning.

Members of the public were not involved and the area was cordoned off.

Rudd said: "The events of this year have shown why it is vital that the emergency services, government and agencies prepare and rehearse our response to potential terrorist attacks.

"The professionalism with which front-line services dealt with the atrocities in London and Manchester is in part due to the planning and practice that goes into exercises like this.

"I will chair a meeting of COBR as part of the exercise and working with colleagues in both the UK and Scottish Governments as we test our plans to keep families and communities across the UK safe."

Scotland's justice secretary Michael Matheson said: "Scotland has a key role to play in hosting this exercise, alongside the UK Government and other agencies.

"It provides an opportunity to test our response in Scotland and the readiness of our emergency services to deal with this kind of incident.

"The Scottish Government shares the commitment of our partners to taking all necessary steps to assess and strengthen our preparedness to deal effectively with terrorism."

He added: "While fortunately such real life incidents are rare, the public can be assured that government, our blue-light services and other agencies are continuously testing and reviewing how we are best able to respond to an attack should it happen."