Kyiv, Ukraine - Former vice president Mike Pence jetted into Ukraine on Thursday to back the embattled nation's fight to repel the Russian invasion amid deep divisions over the war within the Republican presidential field.

After meeting with President Volodymyr Zelensky, Pence called the trip an emotional journey to show firm unity against the "unconscionable and unprovoked Russian invasion."

"I believe America's the leader of the free world," the Republican presidential candidate said. "Coming here ... just steels my resolve to do my part, to continue to call for strong American support for our Ukrainian friends and allies."

Pence visited three Ukrainian towns that were ravaged by Russian occupation, including Irpin and Bucha, which was the site of mass killings early in the invasion.

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"I can really see firsthand the heroism of the Ukrainian soldiers holding the line in those woods, see the heroism of the people here in Irpin that held back the Russian army, to see families whose homes were literally shelled," Pence said.

Pence previously visited the Poland-Ukraine border in March 2022 to spotlight efforts to support Ukrainian refugees fleeing the war.

Pence's visit came against the backdrop of deep divisions among Republican candidates and their right-wing base over supporting Ukraine in its battle against Russian aggression.

Former president Donald Trump, the dominant leader of the race, has repeatedly praised Russian strongman Vladimir Putin and has questioned the need to support Ukraine.

His closest competitor, Florida Governor Ron DeSantis, called the invasion a "territorial dispute," although he later sought to walk back the comments.

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Pence is battling for third place with several other candidates, most of whom say they don't support Putin but believe the billions in aid to Ukraine could be better spent on domestic priorities.

Pence, an old-school conservative and geopolitical hawk, says Americans must understand that failing to stop Russian aggression in its tracks would be far more costly in the long term for the West.

"It's important that the American people understand the progress that we've made and how support for the Ukrainian military has been in our national interest," Pence claimed.

Meanwhile, Greta Thunberg, the Swedish climate activist, was in Ukraine on Thursday and met with President Volodymyr Zelensky to record the environmental damage caused by Russia's war against his country.

Thunberg was in the Ukrainian capital with an international working group whose goal is to help force Russia to compensate for the damage caused by the invasion more than 16 months ago.

"We need your professional help," Zelensky told the delegation.

He pointed in particular to the terrible devastation in the southern Kherson region caused by the destruction of the Kakhovka dam and subsequent floods since early June.

"I don't think the world's response to this ecocide has been sufficient," Thunberg said, according to Ukrainian media. "I don't think any response can be sufficient, because there are simply no words to describe this brutality."

"So I guess we need to make more room for people who are affected by these catastrophes to tell their stories and to share information about what's happening on the ground."

"We must do everything we can to speak out about this and to try to spread awareness and share information about what is happening."

Zelensky also reported problems with drinking and service water supplies in Kherson and the neighboring Mykolaiv region. The agricultural sector and the region's biodiversity have also been damaged.

The environmental working group included the former Swedish vice president Margot Wallström, the former Irish president Mary Robinson, and the Finnish Vice-President of the EU Parliament Heidi Hautala.