Russia-Ukraine updates: US sanctions Russian military shipbuilder, diamond miner

Russian troops "are not withdrawing" from parts of Ukraine as claimed, but rather are "repositioning," according to NATO Secretary-General Jens Stoltenberg, who cited NATO "intelligence."

"Russia has repeatedly lied about its intentions," Stoltenberg said at a press conference Thursday. "Russia is trying to regroup, resupply and reinforce its offensive in the Donbas region [in eastern Ukraine]."

Meanwhile, pressure is being maintained on Ukraine's capital, Kyiv, and other major cities, according to Stoltenberg.

"We can expect additional offensive actions bringing even more suffering," he added.

Videos circulating online show intense fighting taking place in Ukraine's besieged port city of Mariupol.

The footage, verified by ABC News, was taken by a Russian state media journalist who is embedded with the Russian military. The videos were posted online Thursday, though the exact date of filming was unknown. Based on the location of the fighting, ABC News assesses it is highly likely the videos were shot in the past couple of days.

One video shows a Russian tank firing multiple times on the streets of Mariupol. Another video shows the Russian journalist filming himself in Mariupol as tanks open fire and gunshots erupt all around him.

The strategic port city in southeastern Ukraine has been under heavy Russian bombardment for weeks and tens of thousands of civilians remain trapped there.

-ABC News' Fergal Gallagher

Despite Russia's claims of curbing its military activity around Chernihiv, "significant Russian shelling and missile strikes have continued" in the besieged northern Ukrainian city, the U.K. Ministry of Defense said Thursday in an intelligence update.

Meanwhile, Russian forces continue to hold positions to the east and west of Ukraine's capital, Kyiv, "despite the withdrawal of a limited number of units," according to the ministry.

"Heavy fighting will likely take place in the suburbs of the city in the coming days," the ministry added.

Heavy fighting also continues in Ukraine's southern port city of Mariupol, "a key objective of Russian forces," according to the ministry.

"However Ukrainian forces remain in control of the center of the city," the ministry said.

The Russian government is "concerned" by recent statements from U.S. officials claiming that Russian President Vladimir Putin "felt misled" by his advisers and the Russian military on the war in Ukraine, Kremlin spokesman Dmitry Peskov said at a press conference Thursday.

"We do not just regret this. This is a source of our concern," Peskov told reporters, "because such an utter lack of understanding is the reason why erroneous, rash decisions are made with very bad consequences."

"It looks like neither the [U.S.] Department of State nor the Pentagon know what is really happening in the Kremlin," he added. "They simply do not understand what is going on in the Kremlin. They do not understand President Putin. They do not understand the decision-making mechanism. They do not understand our work style."