London (CNN) -- The contractor responsible for providing security guards for the Olympic Games said Saturday it stands to lose up to $77 million after failing to recruit enough staff, less than two weeks before the event opens in London.
G4S chief executive Nick Buckles said he was "deeply disappointed" the firm was unable to live up to its contract with the London 2012 organizing group, LOCOG.
The company has come under heavy scrutiny this week after the government was forced to announce the deployment of 3,500 extra military personnel to cover the shortfall.
The deployment means that 17,000 troops will be on duty in the United Kingdom during the Games, compared with the 9,500 currently in Afghanistan.
G4S had been expected to recruit a staff of about 10,400 as part of a total security force of 23,700 for the Olympic and Paralympic Games.
The contractor said this week that while 4,000 are already at work across 100 venues, more than 9,000 are still going through the training and vetting process.
In a statement Saturday, the company said it had "encountered significant difficulties in processing applicants in sufficient numbers through the necessary training, vetting and accreditation procedures. As a result, we will be unable to deliver all of the necessary workforce numbers."
That failure is likely to cost the firm between £35m and £50m ($54 million -$77 million), it said.
G4S "deeply regrets that, despite the relentless efforts of so many of its people, it is unlikely to deliver in full its obligations to LOCOG, to the government and to everyone with an interest in these Games."
The company will meet the cost of the additional military deployment, it said, and "is also incurring other significant costs as it endeavours to meet the contract challenges."
It also expressed its gratitude to those military personnel who will be deployed on short notice to fill the gap.
"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," Nick Buckles said, quoted in the statement.
Britain is on a heightened state of alert ahead of the Games, which open on July 27.
Home Secretary Theresa May said Thursday that "there is no question of Olympic security being compromised."
But opposition lawmakers have described the situation as a "shambles," saying it raises concerns over the government's grip on the preparations for the Olympics and Paralympics.
LOCOG chairman Sebastian Coe said Friday he was "extraordinarily impressed with" private contractor G4S so far.
Coe said he was happy with the security staff on site and that while G4S has "challenges," it would get there.
Olympic organizers have agreed to give 10,000 tickets to the armed forces to compensate for the short-notice deployment, the Ministry of Defence said.
The questions over security staff come as Britain gears up to welcome many of the visiting teams' officials this weekend ahead of the athletes' arrival on Monday.
One headache was removed for organizers with the reopening Friday of the main highway linking Heathrow airport with central London. The busy M4 motorway had been closed for a week for emergency repairs to a viaduct.