The Polish foreign minister has been filmed telling a Ukranian protest leader: "If you don't support this [deal] you'll have martial law, you'll have the army. You will all be dead."
When asked by ITV News Europe Editor James Mates if he had managed to convince the opposition, Radoslaw Sikorski appeared to reply: "I don't know."
The ministers later returned for further negotiations, after which they announced they had backing from the opposition.
This update has been edited to include video subtitles
More top news
In an email to the actor, Twitter said the tweet “has the potential to be misleading in a way that could impact an election”.
The man was detained by security staff on Sunday evening.
The Duke of Sussex will make a speech at the Loughborough University event.