It is "inevitable" that the UN climate change conference COP26 in Glasgow will cause disruption to day-to-day policing, a review has warned.
The event in November was postponed last year because of the pandemic.
About 10,000 officers from across the UK will be deployed each day during the conference, which is expected to attract 120 heads of state.
Police Scotland said it was "the most complex and complicated" event ever staged in Scotland.
HM Inspectorate of Constabulary in Scotland (HMICS) said the policing plans were "progressing well" for the event at Glasgow's Scottish Events Campus.
The watchdog body said: "Given the complexity and challenge of policing COP26, the size and scale of the event which will put exceptional demand on resources, HMICS believes it to be inevitable there will be an element of disruption in day-to-day policing."
Gill Imery, Chief Inspector of Constabulary in Scotland, said: "It will place significant demands across policing and necessitate the largest mass mobilisation of police officers that has taken place in the UK in many years.
"I am confident the leadership of Police Scotland, its officers and staff are committed to the effective and efficient policing of the event whilst maintaining delivery of business as usual and monitoring and supporting staff wellbeing."
COP26, or the 26th Conference of the Parties, is the key forum for countries all over the world to tackle climate change.
It is hoped the meeting in Glasgow will see countries agree a number of key steps to deal with rising temperatures.
'Iconic world leaders'
Each member of the United Nations has been invited, meaning nearly 120 heads of state are expected to attend along with around 20,000 accredited delegates.
Assistant Chief Constable Bernard Higgins said the event will see "the greatest mass mobilisation of police officers from across the UK" for up to three weeks.
Mr Higgins said US President Joe Biden is among those confirmed to attend, while police believe Pope Francis could also travel to Glasgow.
He said: "If you take the two most iconic world leaders, the president and the pontiff, and put them in one place then the likelihood is that that will absolutely encourage a significant number of other world leaders to attend."
Mr Higgins said Police Scotland, which recently sent some of its officers to the G7 summit in Cornwall, is contributing 45% of the numbers required for COP26.
The huge security operation will involve local policing officers from each of Scotland's 13 divisions and specialist resources, such as firearms officers and dog handlers.