By Stephen Murphy, Ireland correspondent
Former US Secretary of State John Kerry has said he will not seek the Democratic nomination for the 2020 presidential election.
The 75-year-old, who was defeated in the 2004 election by George W Bush, had previously said he was considering a run and wasn't "taking anything off the table".
However, speaking to Sky News at an environmental summit in Cork, Mr Kerry said he would not be entering an already crowded field of 23 candidates for the nomination.
"I was giving it thought at a time when Joe Biden hadn't made up his mind, I wasn't in a rush to have to get into the race then", he said.
"I'm delighted he's in the race as he and I are old friends. I'm hopeful that we're going to wind up with a nominee who will resoundingly be able to help lead the country in a better direction.
"I'm not running; it's not me, that's for sure."
As the keynote speaker at the Our Ocean Wealth summit organised by the Irish government, Mr Kerry also criticised US President Donald Trump's record on climate change issues, and "fake news" surrounding the climate crisis.
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"I think anyone who knows what's happening in America knows that facts are being altered and the truth is not being told with respect to climate change by this administration," Mr Kerry said.
"They block it from being used in the State Department, they block it from being used in the relevant agencies, they've pulled out of the Paris Agreement. Obviously, I'm not a supporter of those choices."
Mr Kerry, who as secretary of state was one of the architects of the Paris Agreement, said Mr Trump's decision to pull the US out of the deal will "cost lives" because it will contribute to a slow response to climate change, and described it as "an enormous mistake on a global basis".
Speaking in the wake of the Brexit referendum in 2016, Mr Kerry said the decision could possibly "be walked back", but today acknowledged that the changing dynamics "make it more likely that there will be some kind of Brexit".