G4S stands to lose up to £50 million as a result of the London Olympics security fiasco, the firm has said.

In a statement, the company said it "deeply regrets" the problems which have meant 3,500 troops being drafted in at the 11th hour to make up a shortfall in security guards.

"G4S accepts its responsibility for the additional cost of the increased military deployment resulting from the shortfall in workforce delivery," the statement said. "The company is also incurring other significant costs as it endeavours to meet the contract challenges.

"Whilst it is not possible to gauge the precise financial impact, it is estimated that the company will incur a loss on the contract in the range of £35 million to £50 million, all of which will fall in the current financial year."

G4S chief executive Nick Buckles expressed regret that the firm had been unable to meet its commitment to the London Olympic Organising Committee (Locog) to provide security guards.

"We are deeply disappointed that we have not been able to fully deliver against our contract with Locog and that it has been necessary to call upon the additional military personnel," he said. "In partnership with the military and Locog, we are working flat out around the clock to resolve the situation. We are determined that together we will deliver a successful and secure games."

In its statement, G4S said it had run into difficulties in processing applicants in sufficient numbers through the necessary training, vetting and accreditation procedures in what it described as "an extremely complex workforce supply contract" on an "unprecedented scale".

"As a result, we will be unable to deliver all of the necessary workforce numbers," it said. "We have worked very closely with Locog throughout the build up. At the point we felt that we could no longer assure the scale of the security workforce we had committed to, we advised them of the situation."

On Friday, David Cameron said that firms who failed to deliver on their contracts to the games should have to bear the cost. The Prime Minister said: "I'm absolutely clear that if companies don't deliver on their contract then they should be pursued for that money."

G4S was initially contracted by organiser Locog in 2010 to provide 2,000 security staff for £86 million, but that figure has since risen to 10,400 personnel in a contract now worth £284 million.