Russia's foreign ministry said Ukraine had used Western rockets, likely U.S.-made HIMARS, to destroy a bridge over the Seym river in the Kursk region, killing volunteers trying to evacuate civilians.

"For the first time, the Kursk region was hit by Western-made rocket launchers, probably American HIMARS," Maria Zakharova, spokeswoman for the Russian foreign ministry, said late on Friday on the Telegram messaging app.

"As a result of the attack on the bridge over the Seym River in the Glushkovo district, it was completely destroyed, and volunteers who were assisting the evacuated civilian population were killed."

Ukrainian army chief Oleksandr Syrskyi said on Friday that Kyiv's forces were advancing between 1 and 3 kilometres (0.6 to 1.9 miles) in some areas in the Kursk region, 11 days since beginning an incursion into Russia.

Kyiv has claimed to have taken control of 82 settlements over an area of 1,150 square kilometres (440 square miles) in the region since Aug. 6. Reuters could not independently verify either side's battlefield accounts.

Russia has accused the West of supporting and encouraging Ukraine's first ground offensive on Russian territory and said Kyiv's "terrorist invasion" would not change the course of the war.

The United States, which has said it cannot allow Russian President Vladimir Putin to win the war he launched in February 2022, so far deems the surprise incursion a protective move that justifies the use of U.S. weaponry, officials in Washington said.

Russia has called the incursion a "major provocation" and vowed to retaliate with a "worthy response," more than 2-1/2 years since it launched a full-scale invasion of its smaller neighbour.

Russia's Defence Ministry said on Friday its troops repelled Ukrainian attacks in several areas, including near the villages of Gordeevka, Russkoe Porechnoe and others.

Zelenskyy hailed Russia's losses in the Kursk region as "very helpful" for Ukraine's defence.

"It concerns the destruction of the Russian army logistics and the draining of their reserves," he said in an evening address.

Kyiv Air Force commander Mykola Oleshchuk added on Telegram that aviation was an active part of the operation, targeting the enemy's supply routes and logistics centres. He posted a video of a strike on a bridge.

Kursk regional governor Alexei Smirnov said Ukraine had destroyed a road bridge over the Seym river in the region's Glushkovsky district.

The heaviest fighting, though, was ongoing in Ukraine's east where Russian troops for months have been inching towards the strategic hub of Pokrovsk.

Analysts said that distracting Russian forces from the east was one of the aims of Ukraine's Kursk operation. But so far there was no indication of letup in the east.

Russian forces were 10 kilometres from the outskirts of Pokrovsk and about 6 kilometres from nearby Myrnohrad, according to local officials.

"If the objective was to divert the Russian effort from the Donbas, it's failed so far," said Yohann Michel, a French military expert and research fellow at the IESD Institute in Lyon, France.

He said Kyiv was aiming to maximise the effect of the Kursk offensive while Russia was trying to do the same in Ukraine's east.

"It's probably the first one who will blink who will have to stop his own offensive," he said.

Zelenskyy said Ukraine was "not for a second" forgetting about the east and promised fresh weapons deliveries - over what was planned — to strengthen the positions.