LONDON, England (AP) — In a one-two punch to hopes for a smooth Olympics, Britain had to put 1,200 extra troops on standby today due to a shortage of security guards and UK border agents decided to strike the day before the games begin.

The last-minute infusion of manpower comes as security contractor G4S continues to fall short of its obligations to provide thousands of guards to protect 100 Olympics-related sites.

Safety is a huge issue for the Olympics, and one that has become a painful embarrassment both for the British government and for G4S, which had promised to provide some 10,400 guards.

G4S acknowledged last week it would be unable to fully staff the games, a last-minute admission that forced the government to call in 3,500 other soldiers to help meet the shortfall.

Today, Jeremy Hunt, the government secretary in charge of the Olympics, acknowledged that even G4S's reduced numbers may not hold up, telling the BBC he had put the extra troops on standby "in the unlikely situation that G4S's performance deteriorates from where it is today."

The seeming inability of government officials to get a proper grip with staffing issues has been compounded by a series of industrial disputes — including one that threatens to lead to a 24-hour-long walkout by border guards at London's Heathrow Airport on July 26, the day before the London Olympics begin.

Even without the strike, London's Heathrow Airport has been beset for months by sporadic long lines at passport control, which the union blames on government spending cuts. The problem had eased in the last week as thousands of Olympic VIPs arrived for the games, but a walkout threatens a return of the endless waits at the worst possible moment for Britain's international image

Hunt's announcement about more troops came as his Cabinet colleague, Home Secretary Theresa May, acknowledged that officials had been warned last month about Olympic security manpower issues, far earlier than has previously been admitted.

In a letter to an opposition lawmaker Keith Vaz, May wrote that she was told of a "possible temporary shortfall" in staffing numbers by G4S as long ago as June 27 and that she had already begun marshaling military resources as a contingency.

That's far earlier than the May 11 date that May had previously mentioned to lawmakers in Britain's House of Commons.