Washington (AFP) - US President Joe Biden announced sanctions against Russia Friday, on over 500 targets, to mark the second anniversary of Moscow's invasion of Ukraine while vowing sustained pressure to stop President Vladimir Putin's "war machine."

The sanctions, described as the largest single tranche since the start of the war, also seek to impose a cost for the death last week in a Siberian prison of Putin's most vocal critic, Alexei Navalny -- with measures taken against three officials.

But they stopped short of potentially game-changing moves under consideration such as funding Ukraine by seizing assets from Russia, whose economy has kept growing despite two years of pressure.

The new economic effort comes as Russia makes its first gains in months on the battlefield in Ukraine, which has been forced to ration ammunition as a political impasse in Washington blocks new US military aid.

Speaking on the eve of the second anniversary since the war started, Biden said: "We can't walk away now."

The latest sanctions notably target the Mir credit card system, set up by Russia to avoid reliance on US-based networks.

The Treasury Department also said it was targeting investment funds and regional banks to hit "Russia's core financial infrastructure."

Key businesses targeted include Russian transportation logistics company JSC SUEK, said to serve the Russian defense ministry, and specialty steel producer Mechel.

Others were in 3D printing, lubricants, robotics and automation. The actions also impact entities and individuals in countries including China and the United Arab Emirates.

The sanctions "will ensure Putin pays an even steeper price for his aggression abroad and repression at home," Biden said in a statement.

"We are also imposing new export restrictions on nearly 100 entities for providing backdoor support for Russia's war machine," he said.

Russia withstanding pressure

The United States and its allies have imposed a slew of measures against Russia since the start of the war, including blocking financial assets, restricting high-tech exports and setting an official cap on the sale price of Russia's oil exports.

Despite US-led pressure, the Russian economy grew by more than three percent last year and is expected to grow again this year, a rate better than some Western nations backing Ukraine.

Russia has adapted and turned to trade with non-Western partners, especially China, even as US officials note that Moscow has less discretionary funding for non-military purposes.

European partners have balked at US-led calls to seize Russian assets and hand the potentially billions in funding to Ukraine, fearing this would lead other governments with questionable reputations to desert Western banks.

Deputy Treasury Secretary Wally Adeyemo said Washington was still working "intensely" with allies to consider options to support Ukraine.

"Fundamentally, we're not going to do anything on Russian sovereign assets until we move as a coalition," Adeyemo told reporters.

A coalition involving the Group of Seven leading economies, the European Union and Australia earlier announced plans to tighten compliance with the $60 per barrel cap on sales of Russian crude, which has been widely circumvented.

To cut Moscow's petroleum revenues and enforce the price ceiling, the Treasury blacklisted 14 Russian oil tankers Friday, while imposing sanctions on state-run shipping company Sovcomflot.

A senior Treasury official told reporters the Kremlin has sought to evade the cap by investing in a "shadow fleet" operating outside coalition financial services -- and that Washington is seeking to raise the cost of using this fleet.

Military aid held up

Biden has also declared that he considers Putin responsible for the death of Navalny, 47, who barely survived a 2020 poisoning he blamed on government agents.

The sanctions on three officials over Navalny's death follow a similar move by Britain. Some European governments also summoned Russian diplomats to lodge protests.

On Friday, the White House said Washington would take further measures in response to Navalny's death, saying fresh sanctions were "just the start."

In announcing the latest measures, Biden made a fresh plea for Congress to fund new military aid for Ukraine.

Republican House Speaker Mike Johnson has refused to bring the aid to a vote with his ally, presidential hopeful Donald Trump, criticizing support for Kyiv.

"History is watching, the clock is ticking, brave Ukrainian soldiers and civilians are dying," Biden said Friday, urging for the bill to be passed.