Ukrainian troops are still fending off Russian and North Korean forces in Russia's Kursk region but face a potential new attack on Ukraine's northeast Sumy region, President Volodymyr Zelenskyy said on Saturday.

Military analysts say Russia is close to ejecting Ukrainian forces from their months-old foothold in the western Russian region, seized in a mass cross-border incursion last August. That prompted U.S. President Donald Trump to warn that thousands of Ukrainian troops were "completely surrounded."

Russia's Defense Ministry said its forces had retaken two more villages near Sudzha, 10 km (six miles) from the Ukrainian border, a town which Moscow said it had recaptured on Thursday.

Russia's Emergencies Ministry said more than 300 residents had been evacuated from areas around Sudzha.

The region's acting governor, Alexander Khinshtein, said officials discussed restoring recaptured areas and establishing how many residents wanted to return to their home settlements.

Zelenskyy said on social media, after being briefed by his top general, that Kyiv's troops were not encircled in Kursk, but that Moscow was accumulating forces nearby for a separate strike.

"This indicates an intention to attack our Sumy region," he said. "We are aware of this and will counter it."

"I would like all (our) partners to understand exactly what Putin is planning, what he is preparing for, and what he will be ignoring."

Russian President Vladimir Putin said on Thursday he supported in principle Trump's proposal for a 30-day ceasefire with Ukraine, but would fight on until several crucial conditions were worked out.

On Saturday, British Prime Minister Keir Starmer said European nations and Western allies were boosting preparations to support Ukraine in the event a peace deal was struck with Russia, with defense chiefs to firm up "robust plans" next week.

"The buildup of Russian forces indicates that Moscow intends to keep ignoring diplomacy," Zelenskyy added. "It is clear that Russia is prolonging the war."

In his statement, he also said the battlefield situation near the strategic eastern Ukrainian city of Pokrovsk had stabilized, and that Ukraine had successfully used a new domestically-produced long-range missile in combat.

Kyiv is seeking to expand its domestic defense industry to wean itself off Western allies who have provided critical artillery, air defense and long-range strike capabilities.

Ukraine's new "long Neptune" missile has a range of 1,000 kilometers, Zelenskyy said.

Russia's Defense Ministry said Moscow's forces had recaptured the villages of Rubanshchina and Zaoleshenka, just outside Sudzha.

Russia has accelerated a push to drive Ukrainian forces out of Kursk, where they seized about 100 settlements last August.

Ukraine's popular DeepState war blog, which tracks the war's front line using open sources, said on Saturday that Russian forces now held Sudzha as well as Rubanshchina and another settlement.

The Ukrainian military's General Staff, in a late afternoon report, made no mention of the situation in Sudzha, but said 11 armed clashes had occurred in Kursk region, with three still going on. Russian forces, it said, had launched 21 airstrikes and 32 guided bombs and shelled Ukrainian positions 150 times.