The Home Secretary said the issues with G4S supplying enough guards initially looked like "teething problems".
Theresa May said: "They were consistently telling us, up until July 11, that they could produce the number of people required for the Olympic Games [they believed they identified] a temporary problem which was capable of resolution.
"We are constantly monitoring, constantly looking at how they are ensuring that safety and security for the Games so the people who come to these Olympic Games enjoy them."
Faced with a list of last minute problems, ministers and organisers insist the Olympic security situation is under control.
Theresa May was tonight accused of giving MPs a "selective account" about when she knew G4S were having problems supplying Olympic staff.
MOD confirm picture of UK Olympics troops sleeping on chairs as they cover the G4S shortfall in Olympic security is genuine