The Guardian newspaper had reported that America planned to send up to 1000 security officers to London for the Games including some 500 FBI agents.
Instead, Mr Allison confirmed that most countries are likely to send "security liaison officers" who will work with British police.
"Some teams, they bring liaison officers with them, they're not protection officers, they're not there for any other reason apart from to be a liaison point with us," he said.
He could not estimate how many such officers will be in London for the Games, but reiterated that only a small number of British police would be armed during the 64-day police operation.
"The basic planning assumption is that there will be no foreign armed personnel here. The planning assumption we're working off at the moment is that the UK will be policed by the British police service and the people empowered to carry guns, thankfully only a few of them, are the British police service," he said.
"The vast majority of officers on the operation will be unarmed. That's what we are on a daily basis."
At the same meeting on Tuesday London 2012 Olympic Organising Committee chief executive Paul Deighton confirmed that the British military will be part of the security operation as the number of personnel required is revised upwards from initial estimates of 10,000.
"We are in the process of reviewing, the number will be increased, we just don't know what the number will be yet," Mr Deighton said of the number of security guards.
"The number that was originally put forward was a number that was used for planning purposes. I always think of it as a stake in the ground, while the venues, transport, accommodation, all the other planning, was put in place. As that planning has turned into real, practical, venue-by-venue, person-by-person planning and we determine just how well the venues need planning ... assumptions turn into reality and it just turns into a higher number."
-AAP