The US leader took to Twitter shortly after the summit in Canada ended on Saturday, accusing Canadian Prime Minister Justin Trudeau of dishonesty and withdrawing Washington's endorsement of the statement which vowed to fight protectionism.
Kudlow said he personally negotiated with Trudeau during the two-day G7 summit in Quebec's Charlevoix region and insisted the USA agreed to the language in the communique in good faith. Later, the document was made public.
Newly sworn Italian Prime Minister Giuseppe Conte said he supports Trump's proposal.
"Canadians. stood shoulder to shoulder with American soldiers in far off lands in conflicts from the First World War onward", the prime minister said at a press conference at the end of the summit.
Trump, who repeated that his tariffs are meant to protect US industry and workers from unfair global competition, told reporters he had suggested to the other G7 leaders that all trade barriers, including tariffs and subsidies, be eliminated.
Trump - who left the summit earlier than scheduled - demanded on Saturday that G-7 countries reduce their trade barriers and has adamantly defended the tariffs on aluminum and steel he placed on USA allies.
The remarks apparently upset Trump, who had left the conference early to travel to Singapore for a highly anticipated meeting with North Korean leader Kim Jong-un.
Trump has imposed tariffs on steel and aluminum imported to the United States from the EU, Canada and Mexico.
Those tweets also centered on trade.
Tariffs, a major point of contention, were taken on in the statement, though in more diplomatic terms than the earlier back-and-forth between Canada and the U.S.
Such a move could make it almost impossible to renegotiate the terms of the 1994 NAFTA pact between the United States, Canada and Mexico. "President Trump is creating chaos".
Representatives from other G7 countries said they felt as though they had made progress in conveying their positions to Trump, something many of them felt pressured to do by voters at home.
He also resumes his criticism against Canada for unfairly charging tariffs on dairy products heading to the United States. The Canadian leader pulled a "sophomoric political stunt for domestic consumption", Kudlow said, that amounted to "a betrayal". The noise of Trump's helicopter landing was so loud they had to stop talking for a while, in a scene one official compared to the opening from the USA television series M.A.S.H.
TRUMP SOT: "We're going to deal with the unfair trade practices". "Tariffs will come way down".
Trudeau, in Quebec City for bilateral meetings with non-G7 leaders after the summit, did not comment as he arrived.
Canada, Mexico and the European Union also are moving ahead with their own levies on USA goods.
"If they retaliate, they're making a mistake", Trump said.
Freeland reiterated Canada will retaliate to US tariffs in a measured and reciprocal way, adding Canada will always be willing to talk.