BUENOS AIRES – President Donald Trump on Thursday canceled a high-stakes meeting with Russian President Vladimir Putin, a stunning decision that he described as a response to Russia’s seizing of three Ukrainian ships over the weekend.

But the move also came just hours after his longtime personal attorney, Michael Cohen, pleaded guilty to lying to Congress about a proposed Trump Tower development in Moscow. Trump has repeatedly denied having business interests in Russia.

"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," Trump tweeted from Air Force One as he flew from Washington to the two-day G-20 summit in Argentina.

"I look forward to a meaningful Summit again as soon as this situation is resolved!"

Though Trump hinted earlier in the week he might cancel the face-to-face with Putin, he was widely expected to go through with it. About 48 minutes before the tweet, Trump told reporters that he would "probably" meet Putin and said he believed it was "a good time to have the meeting." The president also said he intended to review more information about the incident on the flight.

Trump and Putin will now circle each other at the G-20 summit, where the president is expected to focus largely on trade. Just as during their brief encounter in Paris earlier this month, where Putin offered a thumbs-up to Trump that received global attention, any small exchange between the two leaders will likely be closely parsed for meaning.

New Jersey Sen. Bob Menendez, the top Democrat on the Senate Foreign Relations Committee, knocked Trump for canceling.

“I would have liked him to meet Putin and challenge Putin, to find his spine as it relates to Putin’s violation of the international order,” Menendez told CNN. “This was (Trump’s) opportunity to redeem himself … and instead he's abdicating it."

But Sen. Bob Corker, R-Tenn., chairman of the Senate Foreign Relations Committee, said it was fine in his view for Trump to cancel the meeting.

“I do think we need to strongly support Ukraine,” Corker told reporters on Thursday. Corker noted that the Trump administration has provided defensive weapons to Ukraine, something the Obama administration resisted.

“Taking a strong stance now against what Putin is doing, I strongly support that and appreciate it,” he said.

The Kremlin, which had insisted for days that the meeting was still on, indicated Russian officials did not receive confirmation of the cancellation through official channels. A Kremlin spokesperson told a Russian state media outlet that if the meeting was off, Putin would have several hours freed up for other important meetings.

White House press secretary Sarah Sanders told reporters traveling with the president that Russia was made aware of Trump’s decision through “some back and forth,” but she said the president did not speak with Putin about it.

Sanders said Trump made the decision on the flight after conferring with chief of staff Kelly, Secretary of State Mike Pompeo and National Security Adviser John Bolton.

Robert Palladino, the State Department’s deputy spokesman, said Trump’s move would help isolate Russia amid growing international condemnation of its attack on the Ukrainian ships.

“The aggression that we witnessed this week is unacceptable and a strong message been sent,” Palladino said. “They must return to Ukraine its vessels and detained crew members.”

The long-awaited meeting between Trump and Putin was already the subject of intense scrutiny on Capitol Hill, including from fellow Republicans still reeling from Trump's much-criticized performance with the Russian leader in Helsinki this summer. That tension increased amid the diplomatic crisis unfolding after Russia fired on and then seized three Ukrainian ships over the weekend in the Sea of Azov.

"It's just about standing up for what we believe in because I think when you don’t stand up to Russia, or other countries that would take that kind of aggressive activity, they take from it that it’s somehow acceptable,” Ohio Sen. Rob Portman, a Republican on the Senate Foreign Relations Committee, told USA TODAY.

Russia is holding two dozen Ukrainian sailors involved in the skirmish. Ukrainian president Petro Poroshenko has said his country is under threat of "full-scale war" with Russia.

Even before the uncertainty over the meeting, Republican lawmakers were pressing Trump to take a tougher posture with Putin, framing a meeting as an opportunity for a do-over of the heavily criticized appearance at NATO back in July.

At the time Trump, said he believed both sides were to blame for tense U.S.-Russian relations, and he described Putin’s denial that Moscow tried to influence the election as “extremely strong and powerful.” He later walked back part of those remarks, saying he didn’t see any reason why it "wouldn't" be Russia that interfered in the election.

Cohen's plea with special counsel Robert Mueller, who is investigating Russian meddling in the 2016 election, added another twist to what would have been a tricky meeting, in part because it gives an impression that Trump sought help from Moscow.

Trump is set to arrive at the G-20 late Thursday.

The president, who revels in bringing a level of bombast to foreign diplomacy, has frequently made major news on his flights to international meetings like the G-20. Before meeting with British Prime Minister Theresa May in July, he used an interview with a London newspaper to criticize her plan to withdraw from the European Union.

Canceling a high-profile meeting with a world leader is also part of Trump’s playbook. He bagged a summit with North Korean leader Kim Jong Un in May and then, weeks later, agreed to meet with him.