The CIA reportedly has told Mr Trump that Prince Mohammed, who has close ties to the administration, was behind the brutal murder of dissident journalist and U.S. resident Jamal Khashoggi. Since then progress between the two nations appears to have slowed, but Trump continues to hail the meeting as a historic breakthrough.
In tweets sent from aboard Air Force One, Trump said he was doing so because Russia had not returned the Ukrainian boats and sailors it seized after accusing them of illegally entering Russian waters near Crimea.
Tensions had already been high over the war in Syria and allegations of Russian meddling in the 2016 presidential race. He said he would decide on a course afterward. "Maybe I won't even have the meeting".
"I look forward to a meaningful Summit again as soon as this situation is resolved!" he added, Xinhua news agency reported. He stopped short of condemning Russian Federation, instead saying: "I don't like that aggression".
Trump added that he would read a "report" on the plane, seemingly a reference to a status update about Ukraine.
Trump had previously cast the Buenos Aires sit-down into doubt, telling The Washington Post he might cancel seeing Putin after Russia's naval action sparked global condemnation and a sharp escalation in tensions between the neighbours.
His meeting with Putin, which was scheduled to last more than two hours, would have been one of the longest engagements on the President's schedule.
He said they would talk about "strategic stability, arms control and regional conflicts".
Trump's tweet on the meeting was a sudden about-face.
But he seemed to reverse course as he left the White House on Thursday, telling reporters that the meeting with Putin was still on. "It's in the interests of not only our two countries, it's in the interests of the whole world".
Xi said on Wednesday the global community needs to build consensus to solve the conflict between free trade and protectionism.
Like Mr. Trump, Mr. Putin was on his way to Argentina.
"We are in a position to deal with it and handle it very well", he said. "In economic terms we need to decide if we are going to follow the economic globalization and free market or if we are going to choose unilateralism and protectionism". Mr Trump also called national security adviser John Bolton while on board, she said. With so many cooks tending the broth and no real leadership, consensus on trade, capital rules and other issues generally eludes the G-20 leaders. The United States targeted $250 billion in Chinese products, and Beijing lashed back by slapping tariffs on $110 billion worth of USA goods.
"I can say that there was a request, but a conversation did not take place, so to speak", Kremlin aide Yuri Ushakov said.
Kudlow added that if the USA doesn't get "satisfactory" responses to its trade positions more tariffs will be imposed.
Pifer also said Trump could not meet with Putin without addressing the subject of the confrontation with Ukraine.
He said he hoped Berlin could intervene with Ukrainian authorities "to dissuade them from further reckless acts". "Trump in general has a positive attitude".