MOSCOW/KYIV/WASHINGTON (Reuters) -The United States hit Russia's major oil companies with sanctions on Wednesday and accused the Russians of a lack of commitment toward ending the war in Ukraine, as Moscow conducted a major training exercise involving nuclear arms.

Russian President Vladimir Putin has broken his silence on the U.S. sanctions targeting Moscow’s oil industry, calling them “unfriendly” and insisting Russia will not bow to foreign pressure, even as the country faces mounting economic strain.

The Russian foreign ministry accused U.S. Senators of undermining the work of Moscow and Washington on the reunification of Ukrainian children with their families, an effort spearheaded by First Lady Melania Trump.

The European Union on Thursday heaped more economic sanctions on Russia, adding to U.S. President Donald Trump's new punitive measures the previous day against the Russian oil industry. Russian President Vladimir Putin called Washington's move an "unfriendly act" that could backfire by spiking global oil prices.

The Trump administration on Wednesday imposed sanctions on Russia’s two largest oil companies as it called on Moscow to agree to an immediate ceasefire in the war with Ukraine.

The US government jolted energy markets when it sanctioned Russia’s two biggest crude oil producers on Oct. 22. All eyes are now on how the sanctions will affect the supply and price of petroleum across the world.

Kim Jong Un made the comments at the groundbreaking ceremony for a memorial for North Korean soldiers who fought for Russia in its war with Ukraine, state media said.

Ukrainian President Volodymyr Zelenskiy hailed "very important" new U.S. and European Union energy sanctions on Russia on Thursday, but said more pressure would be needed on Moscow to secure a ceasefire in the war.