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

The Pentagon said it's sending six U.S. Navy EA-18 "Growlers" (Navy fighter aircraft equipped with electronic warfare jamming equipment) and 240 personnel to Germany to boost NATO's defenses because of the aircraft's electronic warfare jamming capability.

"They are not being deployed to be used against Russian forces in Ukraine," Pentagon spokesman John Kirby stressed. "They are being deployed completely in keeping with our efforts to bolster NATO's deterrence and defense capabilities along that Eastern flank. They are not being sent because of some sort of acute threat that was perceived or some specific incident that happened."

"This is in order to bolster readiness, enhance NATO's collective defense posture and further increase air integration capabilities with our Allied and partner nations," Kirby said.

-ABC News' Luis Martinez

The Russians appear to be prioritizing the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters on Monday.

“We're not exactly sure what's behind this reprioritization," the official said. This could be Russia refocusing its strategic goals or trying to gain leverage for talks, the official said.

Meanwhile, in the hard-hit city of Mariupol in southern Ukraine, "the Ukrainians are slugging it out" and "keeping the Russians at bay," the official said.

In Kyiv, the situation is static, the official said. Russian troops have stopped making advances toward the capital city, though they continue using their long-range missile fires, the official said.

"We continue to see Ukrainians defend the city and try to push Russians back," the official said.

-ABC News' Luis Martinez

Germany's economy and climate action minister Robert Habeck says G-7 leaders find Russia's demand for "unfriendly" countries to pay for gas in Russia's currency, rubles, "not acceptable."

"All G-7 ministers agreed completely that this would be a one-sided and clear breach of existing contracts," Habeck said Monday, according to The Associated Press.

"Payment in ruble is not acceptable and we will urge the companies affected not to follow Putin's demand," Habeck said, according to the AP.

Habeck said the leaders of the G-7 nations -- Germany, the U.S., France, Italy, Japan, the United Kingdom and Canada -- discussed the issue on Friday.

Radiation levels remain stable in Russia despite fires in the occupied Chernobyl Exclusion Zone, Russian public health watchdog Rospotrebnadzor said Monday.

Rospotrebnadzor said it was continuing to monitor the situation.

The Chernobyl Exclusion Zone is a 1,000-square-mile restricted area of deserted, contaminated land around the shuttered Chernobyl nuclear power plant, the site of the world's worst nuclear disaster in 1986. Russian forces seized the defunct plant and surrounding exclusion zone just hours after launching an invasion of Ukraine on Feb. 24.

The State Agency of Ukraine on Exclusion Zone Management has warned that the radiation hazard is growing due to the blazes in the area, which it said have the potential to spread. The fires observed at more than 30 spots in the Chernobyl Exclusion Zone over the past two weeks have exceeded 8,700 hectares in total, according to the agency.

However, Vadym Denysenko, an adviser to Ukraine's interior minister, said on Monday that the situation was currently "more or less stable."