President Trump on Thursday canceled a one-on-one meeting with Russian President Vladi­mir Putin at the Group of 20 summit in Argentina, a decision he announced just hours after the Kremlin had publicly confirmed the time and date.

In a tweet from Air Force One en route to Buenos Aires, Trump blamed the cancellation on Russia’s seizure of Ukrainian naval ships and sailors in the Black Sea over the weekend. Other top administration officials, including Ambassador to the United Nations Nikki Haley, had condemned Russia’s actions, but Trump had equivocated in recent days.

Trump had signaled in an interview with The Washington Post on Tuesday that he might forgo meeting with Putin after Russia’s naval action sparked global condemnation and a sharp escalation in tensions between Russia and Ukraine.

But he seemed to reverse course as he left the White House on Thursday, telling reporters that the meeting “probably” was still on and that he planned to read a “finalized report” on the Black Sea standoff while on the plane.

Early in the flight, however, Trump, who has a propensity to change his mind, tweeted: “Based on the fact that the ships and sailors have not been returned to Ukraine from Russia, I have decided it would be best for all parties concerned to cancel my previously scheduled meeting in Argentina with President Vladimir Putin.”

“I look forward to a meaningful Summit again as soon as this situation is resolved!” Trump added. A Post reporter was traveling on the plane with the president as part of the press pool.

Trump’s decision was cheered by Ukrainian President Petro Poroshenko. Poroshenko later took to Twitter and wrote in English: “This is how great leaders act!”

White House press secretary Sarah Sanders told reporters on Air Force One that Trump did not make a decision until talking on board with Chief of Staff John F. Kelly and Secretary of State Mike Pompeo, as well as by phone with national security adviser John Bolton, who is in Brazil.

“It’s just happened in the last half-hour,” Sanders said.

Sanders said she was “not aware” whether Trump had directly informed Putin of the cancellation but said that “there was some back-and-forth” through other channels, without elaborating.

Sanders also told reporters that Trump’s scheduled meetings at the G-20 summit with South Korean President Moon Jae-in and Turkish President Recep Tayyip Erdogan would be downgraded to more informal “pull-aside” conversations.

That announcement appeared to surprise South Korean and Turkish officials and left them scrambling to find out more.

“A bilateral meeting will happen between the two presidents in Buenos Aires on the margins of the G-20 summit, as planned and as previously agreed,” one Turkish official told The Post, speaking on the condition of anonymity because of the sensitive nature of the negotiations. “We are not aware of any cancellation or downgrading.”

Trump’s scheduled meetings with the leaders of Argentina, China, Japan, India and Germany appeared to still be moving forward as planned.

Earlier Thursday, Kremlin spokesman Dmitry Peskov had told reporters in Moscow that the meeting between Trump and Putin would take place Saturday around noon.

“We are expecting the two presidents to speak briefly at first, but everything is left to the discretion of the heads of state, Peskov said.

“Washington has confirmed,” he added. 

After Trump’s tweet, Peskov told Russia’s Tass state news agency that the Kremlin had not been informed separately by the White House of the cancellation.

“If this is indeed the case, the president will have a couple of additional hours in his schedule for useful meetings on the sidelines of the summit,” Peskov said of Putin.

A meeting with Putin would have come at a highly sensitive time for Trump politically, with special counsel Robert S. Mueller III’s probe of Russian election interference intensifying back home.

Shortly before Trump departed the White House on Thursday, his former personal attorney Michael Cohen pleaded guilty in New York to lying to Congress about a Moscow real estate project that Trump and his company pursued at the same time that he was running for president.

Lawmakers on Capitol Hill had been bracing for another Trump-Putin sit-down, with some fearing a repeat of last summer’s meeting in Helsinki, after which Trump was widely criticized as appearing too cozy with Putin.

“My fear is the president will put his arm on his shoulder and believe everything Vladimir Putin tells him,” Sen. Richard J. Durbin (D-Ill.) said during a Thursday morning appearance on MSNBC’s “Morning Joe” before Trump announced the cancellation.

Speaking earlier Thursday, Peskov said the agenda for the meeting between Putin and Trump included strategic security, bilateral relations, disarmament and regional conflicts. 

He said American and Russian delegations would also convene for talks that might last an hour. It was not immediately clear whether those talks were still on.

The crisis between Russia and Ukraine has continued to deepen. Kiev is hoping Trump will push Putin on the confrontation, which began Sunday when Russia fired on Ukrainian ships trying to enter the Kerch Strait, a crucial waterway separating the Black and Azov seas. 

But while Russia’s maritime maneuvers have been sharply criticized by senior U.S. and Western officials, Trump earlier this week was more reticent on the issue. He stopped short of condemning Russia, instead saying, “I don’t like that aggression.” 

Martial law is in effect for 30 days in Ukraine, and Russia said Wednesday that it was strengthening air-defense and early-warning radar systems on the Crimean Peninsula, which Moscow annexed from Ukraine four years ago. 

The Kremlin also scoffed at an appeal by Poroshenko for NATO to reinforce the Azov Sea with naval ships, saying this was yet another provocation by Kiev designed to further escalate the situation. 

Ukraine is banking on its Western allies for military support to contain Russia, which Kiev says is preparing to invade Ukrainian territory by land. The latest crisis threatens to significantly worsen an ongoing conflict in eastern Ukraine, where fighting between Russian-backed separatists and Ukrainian forces has resulted in the deaths of 10,300 people sine 2014.

There have been widespread calls for Russia to immediately release the 24 Ukrainian sailors it captured over the weekend, and some European leaders have called for fresh sanctions against Russia. 

But Russia, for the most part, has shrugged off Western pressure. Russia maintains that the crisis was created by Poroshenko for political gain. The deeply unpopular leader could seek reelection in March. 

Wagner reported from Washington. Amie Ferris-Rotman, Anton Troianovski and Natalia Abbakumova in Moscow and William Branigin and David Nakamura in Washington contributed to this report.