Ukraine's President Volodymyr Zelenskyy has urged the nation to unite as Russia continued its attacks on Ukrainian cities over Christmas.

Russian assaults on the weekend in Kherson, southern Ukraine, killed 16 people.

In a video message released on Sunday, Zelenskyy said, "When Ukrainians are together, when Ukrainians are grateful to each other, we cannot be defeated."

Zelenskyy also said, "Russia lost everything it could this year. But it is trying to compensate for its losses with the gloating of its propagandists after the missile strikes at our country, at our energy sector."

Noting that more than 5,500 shelters have already been opened across the country, the president urged people to pay attention to air-raid alarms.

Meanwhile, Russian President Vladimir Putin criticized Ukraine and Western nations in an interview with Russia's state-run television.

Putin said, "We are ready to negotiate with everyone involved about acceptable solutions, but that is up to them -- we are not the ones refusing to negotiate, they are."

He added that 99.9 percent of Russians would be willing to sacrifice their lives for the good of the country.