(Adds comment by Ukraine's Poroshenko)
MOSCOW, Aug 20 (Reuters) - Four people who climbed a Moscow skyscraper on Wednesday and attached a Ukrainian flag to its spire have been charged with vandalism by Russian police and may face three years in jail.
The protesters also managed to paint half a massive yellow star at the top of the spire with blue paint, so it resembled the yellow-and-blue national colours of Ukraine.
Kiev says that Russia, which annexed Crimea in March, is arming separatist rebels in eastern Ukraine. Russia denies this, and says Ukraine is persecuting Russian-speaking citizens.
The flag-flying in Moscow drew comment from Ukrainian President Petro Poroshenko, who is due to meet Russian President Vladimir Putin in Belarus's capital Minsk on Tuesday to discuss the Ukraine crisis together with top European Union officials.
Referring to Kiev's preparations at the weekend for Independence Day and national flag celebrations, he said in a video clip on his Facebook page: "I like very much the fact that, on the eve of celebrating the Ukrainian flag, one of Moscow's highest buildings was painted in our colours."
"I congratulate these Ukrainians," he said, with a smile.
After the four were arrested, maintenance crews quickly removed the flag from the Stalin-era building, which towers over the Moscow River and houses businesses and apartments, and were starting to remove the blue paint.
A photograph on social media, which could not be verified independently, showed a man in a climbing harness, standing on top of the star, with the Ukrainian flag tied to one of its points. He appeared to be taking a "selfie".
An official in the Moscow police press office said the suspects were two men and two women. No details on the circumstances of the arrest were immediately available.
Opinion polls show that most Russians back Russian President Vladimir Putin's policy on Ukraine wholeheartedly, though a minority believes he is isolating Russia. (Reporting by Ludmila Danilova; Additional reporting by Natalia Zinets and Richard Balmforth in Kiev; Writing by Christian Lowe; Editing by Louise Ireland)