MOSCOW - The Kremlin said Thursday that Washington confirmed a one-on-one meeting between President Donald Trump and Russian leader Vladimir Putin atthe Group of 20 summit in Argentina, but Trump later announced that he was canceling the meeting.

In a tweet from Air Force One en route to the summit in Buenos Aires, Trump blamed the cancellation on Russia's seizure of Ukrainian ships and sailors over the weekend.

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 neighbors. But he seemed to reverse course as he left the White House on Thursday, telling reporters that the meeting with Putin was still on.

Shortly afterward, however, Trump 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!"

Earlier, Kremlin spokesman Dmitry Peskov told reporters in Moscow: "We are expecting the two presidents to speak briefly at first, but everything is left to the discretion of the heads of state."

"Washington has confirmed," he added.

As he left the White House on Thursday en route to Argentina, Trump said: "I probably will be meeting with President Putin. We haven't terminated that meeting." He added that he would be getting a "finalized report" on Ukraine while on the plane.

Peskov said the agenda for the meeting scheduled for Saturday between Putin and Trump included strategic security, bilateral relations, disarmament and regional conflicts. "This is in the interests of not only our two countries, but the world at large," he said.

He said American and Russian delegations would also convene for talks that may 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 has been more reticent on the issue. He stopped short of condemning Russia, instead saying, "I don't like that aggression."

Limited martial law in Ukraine is in place for 30 days, and Russia said Wednesday 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 Ukrainian President Petro 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.

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

There have been widespread calls for Russia to immediately release 24 Ukrainian sailors it captured, 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 a vote in March.

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The Washington Post’s Natalia Abbakumova in Moscow and John Wagner and William Branigin in Washington contributed to this report.