Donald Trump has abruptly cancelled a meeting with Vladimir Putin in a show of disapproval at Russia's treatment of Ukraine.
The move, which comes after Russia opened fire on Ukrainian vessels this weekend, casts new uncertainty over US-Russian ties.
"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!" Mr Trump tweeted.
Hours earlier, the Kremlin said the meeting at the G20 summit in Argentina this week was on track.
….in Argentina with President Vladimir Putin. I look forward to a meaningful Summit again as soon as this situation is resolved!
— Donald J. Trump (@realDonaldTrump) November 29, 2018
Dmitry Peskov, Mr Putin's press secretary, was quoted as saying that the Kremlin only learnt about the cancellation from Mr Trump's tweet by Russian media.
He said the cancellation means that Mr Putin will have "a couple more hours" for "useful meetings" with other leaders of the world's 20 largest economies.
White House spokeswoman Sarah Huckabee Sanders said the US leader made the decision to cancel while aboard Air Force One before take-off from Washington to Buenos Aires.
He made the decision after speaking with secretary of state Mike Pompeo and White House chief of staff John Kelly. Mr Trump also called national security adviser John Bolton while on board, she said.
Ms Sanders said that the US and Russian governments had exchanged phone calls.
She told reporters travelling with Mr Trump on Air Force one that he will speak informally with the leaders of Turkey and South Korea at the summit, rather than in formal meetings.
She did not say why the meetings with Recep Tayyip Erdogan and Moon Jae-in had been downgraded.
Mr Trump told The Washington Post earlier this week that he might cancel his meeting with Mr Putin over the conflict with Ukraine.
On Sunday, Russia seized three Ukrainian vessels and crews, injuring six sailors.
Russia said Ukraine did not have permission to pass between Russia's mainland and the Crimean Peninsula. Ukraine argued its vessels abided by maritime laws.
The Kremlin previously said Mr Trump and Mr Putin were meant to talk about an array of issues including nuclear arms control.
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Mr Peskov had said they would start with one-on-one talks and then continue broader negotiations with officials from both sides.
He said they would talk about "strategic stability, arms control and regional conflicts".
Donald Trump has abruptly cancelled a meeting with Vladimir Putin in a show of disapproval at Russia's treatment of Ukraine.
The move, which comes after Russia opened fire on Ukrainian vessels this weekend, casts new uncertainty over US-Russian ties.
"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!" Mr Trump tweeted.
Hours earlier, the Kremlin said the meeting at the G20 summit in Argentina this week was on track.
….in Argentina with President Vladimir Putin. I look forward to a meaningful Summit again as soon as this situation is resolved!
— Donald J. Trump (@realDonaldTrump) November 29, 2018
Dmitry Peskov, Mr Putin's press secretary, was quoted as saying that the Kremlin only learnt about the cancellation from Mr Trump's tweet by Russian media.
He said the cancellation means that Mr Putin will have "a couple more hours" for "useful meetings" with other leaders of the world's 20 largest economies.
White House spokeswoman Sarah Huckabee Sanders said the US leader made the decision to cancel while aboard Air Force One before take-off from Washington to Buenos Aires.
He made the decision after speaking with secretary of state Mike Pompeo and White House chief of staff John Kelly. Mr Trump also called national security adviser John Bolton while on board, she said.
Ms Sanders said that the US and Russian governments had exchanged phone calls.
She told reporters travelling with Mr Trump on Air Force one that he will speak informally with the leaders of Turkey and South Korea at the summit, rather than in formal meetings.
She did not say why the meetings with Recep Tayyip Erdogan and Moon Jae-in had been downgraded.
Mr Trump told The Washington Post earlier this week that he might cancel his meeting with Mr Putin over the conflict with Ukraine.
On Sunday, Russia seized three Ukrainian vessels and crews, injuring six sailors.
Russia said Ukraine did not have permission to pass between Russia's mainland and the Crimean Peninsula. Ukraine argued its vessels abided by maritime laws.
The Kremlin previously said Mr Trump and Mr Putin were meant to talk about an array of issues including nuclear arms control.
More from Donald Trump
Mr Peskov had said they would start with one-on-one talks and then continue broader negotiations with officials from both sides.
He said they would talk about "strategic stability, arms control and regional conflicts".
