Russia’s Wagner paramilitary group claimed on Saturday to have gained control of Bakhmut, the eastern Ukrainian city that has seen the fiercest battles recently in Moscow’s war on Ukraine, but Kyiv disputed the assertion and said heavy fighting continued there.

Yevgeny Prigozhin, Wagner’s leader, said in a video posted on Telegram that Bakhmut came under complete Russian control around midday Saturday, according to media reports.

“Today, at 12 noon, Bakhmut was completely taken,” Prigozhin said in the video. “We completely took the whole city, from house to house.”

Ukrainian officials denied that Wagner had established complete control in Bakhmut, but called the situation in the city critical. Serhiy Cherevatyi, spokesman for Ukraine’s eastern command, told the Associated Press that Prigozhin’s claim “is not true.” Ukrainian “units are fighting in Bakhmut,” he added.

Ukrainian Deputy Defense Minister Hanna Maliar said heavy fighting was continuing in the city. “The situation is critical,” she said. “As of now, our defenders, control certain industrial and infrastructure facilities in this area.”

The developments in eastern Ukraine came as Ukrainian President Volodymyr Zelenskyy arrived in Japan on Saturday for talks with the leaders of the world’s most powerful democracies aimed at shoring up support for Ukraine’s defense against Russian President Vladimir Putin’s 15-month invasion of the country. Bolstering international support is a key priority as Ukraine prepares for an expected major counteroffensive to retake territory seized by Russia.

The British Ministry of Defense said on Saturday that Moscow appeared to be focusing on the battle around Bakhmut, where fighting has raged for more than eight months. “In the last four days, Russia has highly likely redeployed up to several battalions to reinforce the Bakhmut sector,” the ministry said.

“This follows Ukrainian tactical gains on the flanks of the contested Donetsk Oblast town through mid-May and publicly aired doubts about the commitment of Wagner Group forces to continue fighting in the sector,” the ministry said. “The redeployment represents a notable commitment by the Russian command,” it added.

“Russia’s leadership likely continue to see capturing Bakhmut as the key immediate war aim which would allow them to claim some degree of success in the conflict,” the British ministry said.

Prigozhin said his forces would pull out of Bakhmut in five days and hand the ruins of the city over to the regular Russian military, Reuters reported.