I didn’t find any reliable source about that claim. But I knew, the Ukrainian President didn’t mention any decision to close the straits to Russian warships. I thought this is just a request. Seemed like this tweet got misunderstood. It is like a “Thanks for advance” message. Because there was no special decision about banning the passage of Russian warships.
So I recieve information through some journalists about that Senior Turkish official told Turkey has not closed the Bosphorus and Dardanelles to Russian warships. As a result, tweet by Zelensky suggesting otherwise seems to be a misunderstanding.
Another poiny that Montreux Convention gives a clear right to Russians to return their ships to their original ports in Black Sea even in the time of war, even Moscow is belligerent. So can not way any ban or block.
I think Zelensky wanted to form public opinion and political oppression by considering the Turkish density in his country. However, he failed. Some journalists and news sites distorted this tweet by generating false information. Unnecessary noise has been avoided, thanks to people who have done a lot of fact-checking. After warning the journalists who announced that we were closing the Bosphorus and Dardanelles, many journalists deleted their tweets containing misinformation.
Be careful, If you are a journalist, you must fact-check everything and correct your mistakes as soon as you discover it. There is good article about ethical considerations for journalists at Poynter.