The extra money will come from the remaining £1.25 billion contingency fund but the overall cost will stay within the £9.3 billion budget. Organisers added they hope some of the cost will be offset by savings elsewhere.
Following a government review, the Olympic Delivery Authority (ODA) has been given additional responsibility for security and operations between 2011 and 2013, which will cover testing, Games time and the immediate legacy.
"As we enter the busiest and most exciting phase of the Olympic project so far, this report shows we are still on time and still on budget," Olympics minister Tessa Jowell said in a statement.
The security cost is separate to the £600 million budget put aside for securing the Games, such as policing.
