London Olympics organizer defends security contractor

London (CNN) -- The chairman of the London 2012 organizing group Friday rejected concerns over security staffing ahead of the Olympic Games, which start in two weeks.

Sebastian Coe told reporters he was "extraordinarily impressed with" private contractor G4S so far.

His comments follow the announcement by the British government Thursday that an extra 3,500 military personnel are needed to cover a shortfall in recruitment by G4S.

Coe said he was happy with the security staff on site and that while G4S has "challenges," it will get there.

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No one can underestimate the task ahead, he said.

Coe would not comment on the "robust" contract the organizing committee (LOCOG) has with G4S.

Home Secretary Theresa May addressed the issue Thursday. "There is no question of Olympic security being compromised," May said.

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She said it became clear Wednesday that G4S was not able to provide all the security staff it had promised to the organizers of the London Olympic Games.

The government's decision to bring in additional troops, on top of the 13,500 already agreed, was the appropriate response to the shortfall in G4S staff, she said.

The deployment means 17,000 troops will be on duty in the United Kingdom during the Games, compared with the 9,500 currently in Afghanistan.

G4S had been expected to recruit a staff of more than 10,000 as part of a total security force of 23,700 for the Olympic and Paralympic Games. It will still provide several thousand personnel.

A G4S statement Thursday said the company has about 4,000 people at work across 100 venues and has more than 9,000 others going through the required vetting, training and accreditation process.

British newspaper reports Friday highlighted concerns over the training given to G4S recruits and the use of thousands of young people in security roles.

G4S said the scheme to involve young people was run by LOCOG and was aimed at students.

"While they form a vital part of the security workforce, they will be performing more of a support function than the trained security personnel from G4S, or the armed forces," a spokesman said in a statement.

Young people do a "fantastic job" in a similar role at the annual Wimbledon tennis championships, and there's no reason to think they won't perform well at London 2012, the spokesman said.

Britain is on a heightened state of alert ahead of the Games, which open on July 27.

CNN's Jim Boulden and Laura Smith-Spark contributed to this report.