By Dan Peleschuk and Nick Starkov

KYIV (Reuters) -Ukraine's President Volodymyr Zelenskiy called on world leaders on Saturday to show solidarity and unity in supporting Israel and condemning the "terrorist attack" by Palestinian Islamist group Hamas.

Prime Minister Benjamin Netanyahu vowed "mighty vengeance" after a surprise assault by Hamas killed more than 200 people in the deadliest day of violence in Israel in half a century.

Zelenskiy, whose army has been fighting a war Russia launched against it 19 months ago, said that Israel - just like Ukraine - has "every right" to protect itself.

"Let the value of human life and the intolerance of terror be the principles that will finally unite the whole world," Zelenskiy said in his nightly video address.

"Wherever they aim their missiles and whomever they attack, terrorists must lose. And this is important for the whole world."

Ukraine's relations with Israel have been tense since Russia's invasion began in February 2022. While having sent tons of humanitarian aid to Ukraine, Netanyahu has consistently refused to supply weapons to Kyiv.

Israel, a major U.S. partner, has some of the closest ties with Russia among countries politically aligned with the West.

In a much more restrained message than Ukraine, Russia called on both Palestine and Israel to "implement an immediate ceasefire" and said it was in contact with Israel, the Palestinians and Arab countries over the violence.

The Ukrainian army put out a video on Saturday with Ukrainian soldiers condemning the Hamas attack and speaking in support of Israel.

"Every life matters, both in Israel and in Ukraine," one solder said while another added, "This is a crime against the civilized world."

(Reporting by Dan Peleschuk and Nick Starkov;Writing by Dan Peleschuk and Lidia Kelly; Editing by Jason Neely and Lisa Shumaker)