London - British Prime Minister David Cameron said on Thursday on the eve of the opening of the London Olympics that his top priority for the Games is their safety and security.
"The biggest concern has always got to be a safe and secure Games," Cameron told a press conference at the Olympic Park in east London. "That matters more than anything else."
"I think we've made as many preparations as we can, I think we have very good contingency plans in place.
"Always as prime minister I feel that is an area I should take personal responsibility for."
Cameron was responding after US presidential candidate Mitt Romney, who is visiting London and was due to meet the British leader later on Thursday, said he had heard "disconcerting" reports about security.
A security force of more than 40 000 military and civilian personnel, backed by a huge intelligence operation, is being deployed to protect venues, athletes and millions of visitors.
But the government has had to call up thousands of extra troops for the Games after private security firm G4S said it could not provide the 10 000 guards promised.
The prime minister said it was the largest security operation in Britain's peacetime history.
"Our absolute top priority must be to keep people safe," Cameron said.
"There are extra police in the streets of London, in the skies above and in the water of the Thames and they are backed by the finest armed forces in the world.
"We have our intelligence services working aournd the clock... This is the biggest security operation in our peacetime history bar none and we are leaving nothing to chance."
London was hit by terror attacks on its transport network on 7 July 2005 - the day after it was awarded the right to stage the 2012 Olympics.