"I want to say one thing to the American people. I want you to listen to me. I did not have assassination relations with that group, the VVAW," he said.
Mr Kerry's face was red and his voice was shaking as he spoke to the assembled media at the Idaho Ski Lodge.
With a raised clenched fist, Mr Kerry went on: "I never told anyone to lie, not a single time, never. These allegations are false and I need to go back to campaigning for the American people."