Concerns have been raised over a "real risk" security costs for the Glasgow 2014 Commonwealth Games will increase.
According to public spending watchdog Audit Scotland, the Games are generally on track, but "there are risks to particular projects".
Security was a particular concern highlighted in the second progress report by the public body, given the rising costs at previous sporting events.
The budget for the games approved last November was £524m, which was a substantial increase on the initial £373m budget approved by the Scottish Parliament in 2008.
In the report released on Thursday, the budget "remains inherently uncertain as would be expected at this stage."
The report continues: "By September 2011, only 17% of costs were certain, with £44 spent and a further £44m contracted.
"Approximately £142m (39%) of the budgeted operational costs are particularly uncertain as they are based on many unknown factors and early planning assumptions.”
According to Audit Scotland, the distribution of the £27m allocated to security costs is unclear, which puts it “particularly at risk of cost increases” compared to the budget for previous Commonwealth and Olympic Games.
The report concludes that organisers should do more work "to inform the procurement approach for security guards and equipment."
Audit Scotland cited the 2002 Manchester Commonwealth Games as an example as its security budget increased by £3m, which was part of a 120% rise in the overall budget.
Audit Scotland also found "particular risks" for organisers in delivering the athletes' village in Dalmarnock and Hampden Park developments on budget and on time as they are due to be completed less than five months before the Games.
The watchdog found that preparations for the Games are progressing well, with 92% of the milestones due for completion, and the rest "mostly insignificant". It said that the risks were not as high as at other large sporting events as many of the venues and infrastructure were already in place in Glasgow.
In response, a Glasgow 2014 Organising Committee spokesman said: "We welcome Audit Scotland's assessment that progress in planning for the Glasgow 2014 Commonwealth Games is on track.
"We are pleased the progress report also recognises that, with 70% of infrastructure already in place, the risks around delivering Glasgow 2014 are less than for other Games.
"As identified in this report there are risks associated with delivering a complex multi-sport event of this scale. However we are pleased to note the auditor general's comments that partners are identifying key risks and managing them."
More About Glasgow 2014
- More than one thousand people hired to work at Glasgow 2014 Games
- City shopping district to become race track during Glasgow 2014
- Glasgow 2014: Commonwealth Games cultural programme unveiled
- Fake Glasgow 2014 lottery 'winnings' scam targeted in police raid
- Commonwealth Games announces deal to fund sporting scholarships
- Hampden Park turf removed to make way for Glasgow 2014 track
- G4S among security firms providing guards for Commonwealth Games