Nick Clegg said police have been "double, triple, quadruple checking" security arrangements ahead of this weekend's London marathon.
The Deputy Prime Minister insisted everything possible is being done to ensure the event passes off safely following the Boston Marathon bombings.
During his weekly LBC 97.3 radio phone-in, Mr Clegg said the images from the US were "heartbreaking" and that he understood people were anxious.
"I have spoken to the Met Commissioner himself [Sir Bernard Hogan-Howe] about this yesterday, and I have a huge amount of confidence in the police and security services of this country", he said. "They do an amazing job keeping us safe all the time".
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