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".

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, 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 organizers should do more work "to inform the procurement approach for security guards and equipment."

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.