United States President Donald Trump on Thursday cancelled a meeting with his Russian counterpart Vladimir Putin at the G-20 summit in Buenos Aires, Argentina. Trump cited Russia’s seizure of Ukrainian vessels earlier this week as the reason for cancelling the meeting.

“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,” the US president tweeted. “I look forward to a meaningful summit again as soon as this situation is resolved!”

White House spokesperson Sarah Huckabee Sanders said Trump will speak only informally with Turkish President Recep Tayyip Erdogan and South Korean President Moon Jae-in, AP reported. She said Trump made the decision not to meet Putin after advice from Secretary of State Mike Pompeo, Chief of Staff John Kelly and National Security Advisor John Bolton.

Putin’s spokesperson Dmitry Peskov said the Kremlin, the official residence of the Russian president, had not yet received any official information on the cancellation of the meeting. “If this is so, he [Putin] will have a couple of additional hours on the programme for useful meetings on the sidelines of the summit,” Peskov told TASS news agency.

Ukraine had declared the imposition of martial law in its border regions for a month from November 28, a day after Russia seized three of its navy vessels off the Crimean Peninsula. Ukraine said six of its soldiers were injured after a Russian border guard vessel allegedly rammed one of its tugboats in the Kerch Strait, a narrow body of water that gives access to the Sea of Azov and is used by both nations. Russia had annexed the Crimean Peninsula in 2014. However, Russia claimed it had been forced to act as Ukrainian ships illegally entered its waters to “intentionally” provoke a conflict.