The United States plans to slap new sanctions on Russia this week that the White House says will target people and companies inside President Vladimir Putin's "inner circle," Reuters reported.

Washington also plans to impose new restrictions on high-tech exports to Russia's defense industry in a move aimed at punishing Moscow for not living up to an agreement to defuse the situation in eastern Ukraine, where armed pro-Russian activists seized about a dozen government buildings.

The leaders of the Group of Seven (G7) major economies agreed on Saturday, April 27 to swiftly impose further sanctions on Russia over the Ukraine crisis. The United States and European Union previously imposed limited sanctions on Russian officials over Moscow's annexation of Crimea.

Washington could announce its new list of sanctions as early as Monday, senior U.S. officials have said.

The White House said previously that "cronies" of Putin and the companies they control would be targeted with sanctions.

The European Union is also expected to announce sanctions as early as Monday targeting individuals and companies. Washington is more hawkish on further sanctions than Brussels, which has caused some impatience among some U.S. officials with the European response.

The top Republican on the U.S. Senate Foreign Relations Committee said the Obama administration's sanctions on Russian individuals had not gone far enough.

"I think we need to put sectoral sanctions in place," Senator Bob Corker told CBS. "To me, hitting four of the largest banks there would send shockwaves into the economy. Hitting (Russian gas giant) Gazprom would certainly send shockwaves into the economy," he said.

The Western-backed government in Kyiv accuses the Kremlin of planning to invade the east of Ukraine, and of preparing the ground by training and supporting the armed activists.

Russia denies it is to blame for the crisis, saying Ukraine's east is rising up in a spontaneous protest against what it calls an illegitimate government in Kiev.