Britain will deploy an extra 1,200 troops to the London Games, Olympics minister Jeremy Hunt announced Tuesday, following a shortfall in the numbers of guards provided by private contractor G4S.

The extra troops, who were already standing by on 48 hours' notice, bring the total military deployment at the 2012 Olympics to 18,200.

The decision was taken at a cabinet committee meeting chaired by Prime Minister David Cameron, with just three days left before the Games officially open.

While the numbers of security staff being provided by the beleaguered G4S continues to rise, ministers wanted to "leave nothing to chance", Hunt said.

"Security staffing levels at venues have been kept under constant review," Hunt said.

"G4S numbers continue to rise significantly and we have every expectation that will continue to be the case. However, ministers decided that we should deploy the additional 1,200 troops that were put on standby last week.

"On the eve of the largest peacetime event ever staged in this country, ministers are clear that we should leave nothing to chance.

"The government continues to have every confidence that we will deliver a safe and secure Games."

Britain had already drafted in an extra 3,500 troops at late notice to replace the G4S shortfall, taking the numbers on "Operation Olympics" to 17,000.

Around 11,800 of them were from the army, with 2,600-odd each from the Royal Navy and the Royal Air Force (RAF).

At peak times, around 11,000 personnel will be performing security duties at the Olympic venues across London and beyond.

Some units and individuals who returned from operations in Afghanistan earlier this year are involved in supporting the Games but all have completed their post operational tour leave.

The 1,200 troops on standby were at their regular bases, having been brought down from one week's notice to 48 hours.

Some 10,500 athletes will take part in the Games.