Private security firm G4S initially suggested its problems supplying Olympic guards were "teething problems" which would be resolved, Theresa May has said.
On a tour of the Olympic Park's security centre, the Home Secretary said G4S, the world's second largest private sector employer, told officials last month that any problems were temporary and would be sorted out.
She denied being selective in what she told MPs, insisting that the gap in the numbers only became clear on July 11, not two weeks earlier when the firm first reported problems.
Mrs May said that at the start of the month G4S's problems looked like "teething problems" which they would resolve.
"Crucially, it was not until July 11 that G4S finally said 'Actually we can't resolve those initial problems, we won't be able to provide the personnel'," she said.
Asked what the Home Office was told at a meeting with G4S and Olympic organisers Locog on June 27, Mrs May added: "What happened was there were some early signs of a problem with rostering staff for G4S.
"It was clear that G4S felt they were capable of dealing with that, that it would be resolved, and it was on July 11 as the chief executive of G4S told Parliament, the Home Affairs Select Committee, that G4S said 'Actually, we now believe we cannot produce the staff we were contracted to produce'."
Asked if G4S should have acted sooner, Mrs May said they believed they had identified a "temporary problem which was capable of resolution".
During the visit to the control room with Scotland Yard commissioner Bernard Hogan-Howe and London 2012 chairman Lord Coe, Mrs May saw G4S staff and others at work in front of a bank of more than 30 large screens covering the park.
She also met Colonel Gary Wilkinson, the venue's senior military representative, and Superintendent Neil Seabridge, the Met's bronze commander at the park on Friday.