Donald Trump last night said he misspoke when he failed to blame Russia for interfering in the US election in 2016 during a joint press conference with Vladimir Putin in Helsinki.
Mr Trump said he had been surprised by the firestorm of criticism that followed his remarks, and that confusion had been caused by one misplaced word.
At the Helsinki press conference Mr Trump said "I don’t see any reason why it would be" Russia that meddled in the US election, despite all his own intelligence agencies having concluded that it was.
On Tuesday, Mr Trump made a statement at the White House that he had meant to say the opposite.
The president said he wanted to "clarify a key sentence" he spoke in Helsinki. He said that sentence should have been "I don't see any reason it wouldn't be" Russia. He called the sentence he meant to say a "bit of a double negative".
Mr Trump added: "I used the word 'would' instead of 'wouldn't'. I think that probably clarifies things pretty much by itself."
The president said he thought the summit had gone well and was initially confused by the angry reaction, asking himself "What's the big deal?"
He then looked at a transcript of his answers and realised he had misspoken, he said.
The president added that he had "full faith and support" in US intelligence agencies and accepted their conclusion that Russia was to blame.
He said his administration would move aggressively to repel any efforts to interfere in the US mid-term congressional elections in November.
While accepting that Russian election interference "took place" Mr Trump also added: "Could be other people also. A lot of people out there."
Mitch McConnell, the Republican leader in the US Senate, had publicly countered Mr Trump's Helsinki comments just before he issued his clarification.
Mr McConnell said: "There is indisputable evidence that they tried to impact the 2016 election."
He also offered a direct message of support to America's allies in Europe, calling Nato the "most significant military alliance in history".
Trump and Putin | In talks
Mr McConnell said: "Make no mistake about it. I would say to our friends in Europe - we understand the Russian threat. That is the widespread view here in the US Senate . The European countries are our friends and the Russians are not.
"I think it's important for our friends and allies to hear from us. These alliances, painstakingly made in the wake of World War II, are important and we want to maintain them."
Mr Trump had initially been buoyant after the press conference, believing his summit with Mr Putin to have been a success.
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But when he saw television coverage on Air Force One on his way home he reportedly became furious and vented at aides about the lack of support he was getting even from his staunchest supporters.
Anthony Scaramucci, his former communications director, said Mr Trump made a "strategic mistake" and needed to "reverse course".
Newt Gingrich, the former Republican House Speaker, called it "the most serious mistake of his presidency," which "must be corrected immediately".