WATCH: Pentagon press secretary John Kirby holds briefing as Russian forces move towards Kyiv

Pentagon spokesman John Kirby said Russian forces have their sights set on Ukraine’s capital city of Kyiv.

Watch Kirby’s remarks in the player above.

“We also have seen Ukrainians resisting quite effectively around Kyiv and continuously,” he said, making it harder for Russian troops to move south.

The first round of talks aimed at stopping the fighting between Ukraine and Russia have ended with no agreement except to keep talking, while an increasingly isolated Moscow has run into unexpectedly fierce resistance on the ground and economic havoc at home.

“This is day five, and it’s clear the Russians have not made the progress that they wanted to make by day five,” Kirby said.

Russian President Vladimir Putin also put his nuclear forces on increased alert on Sunday in a major escalation of tensions with the West.

Kirby said the announcement was “as unnecessary as it is escalatory.”

The U.N. human rights chief said at least 102 civilians have been killed and hundreds wounded in more than four days of fighting — warning that figure is probably a vast undercount — and Ukraine’s president said at least 16 children were among the dead.

Kirby called Russia’s invasion a “war of choice” on “a neighboring nation state that presented no threat.”

“We know there’s casualties on both sides of this conflict,” he said. “All the blood is on Mr. Putin’s hands.”

More than a half-million people have fled the country since the invasion, another U.N. official said, with many of them going to Poland, Romania and Hungary. Millions have left their homes.