WASHINGTON — The United States is expected to impose additional sanctions against Russia by Friday, according to U.S. officials.



The sanctions are economic and designed to target oligarchs with ties to President Vladimir Putin, the officials said. The final number facing punitive action remains fluid, the U.S. officials said, but is expected to include at least a half a dozen people under sanctions powers given to the president by Congress.



In recent weeks, President Donald Trump's national security advisers have pushed for more sanctions after a series of alleged moves by Russia, including the poisoning of a former Russian spy in England, interference in the U.S. 2016 elections and a cyberattack described as the most destructive and costly in history.



Officials spoke about the sanctions on the condition of anonymity because they were not authorized to discuss pending actions.



On Tuesday night, outgoing national security adviser H.R. McMaster called on the United States to take a tougher line against Moscow, saying, "We have failed to impose sufficient costs."



The remark came hours after President Trump said in a White House news conference that "nobody has been tougher on Russia than I have."



Russian officials, meanwhile, have expressed exasperation with the United States. Moscow's ambassador to the United States, Anatoly Antonov, said the "atmosphere in Washington is poison."



"It's a toxic atmosphere," he told NBC News.



The United States is expected to target individuals on a list of influential Russian political and business leaders that the Treasury Department released in January, officials said.



The United States could also impose sanctions based on authorities Congress granted to target anyone conducting significant business with Russian intelligence and defense sectors.



"If they do something tough like this, it may go some distance in reassuring angry members of Congress and the public who are looking at the midterms and wondering if this administration is focused on the Russian threat and taking moves to address it," said Liz Rosenberg, a former Treasury official who is at the Center for a New American Security.



White House and State Department spokesmen declined to comment.



The pending Treasury move comes as the Trump administration takes an increasingly tough posture toward Moscow at the urging of his senior aides and top U.S. allies.



Last week, the United States expelled 60 Russian spies and diplomats in response to the poisoning of a former Russian spy in Britain, the largest expulsion of Russians in U.S. history.



In early March, the administration also slapped fresh sanctions on Russian government hackers and spy agencies for interfering in the 2016 election and a devastating cyberattack.



In recent days, the Trump administration has contemplated additional actions to publicly condemn Russian aggression. Last Friday, the U.S. ambassador to Russia, Jon Huntsman Jr., told administration officials that he wanted to hold a news conference in Moscow about Russia's expulsion of U.S. diplomats from the country, according to officials familiar with the matter.



Ultimately, the administration chose not to hold the news conference for reasons that remain unclear, but Huntsman did appear in a YouTube video explaining Washington's decision.



In Congress, the Trump administration continues to face pressure from Russia hawks in both parties to take aggressive action against Putin. In an interview, Sen. Lindsey Graham said that while he admired the administration's moves, he believed they had been tried by other administrations and had failed. He said the United States needed to build an alliance of countries that rely on Russia for oil and gas and help them find new opportunities.



"We have to hit them by taking away their customers," he said.



The Washington Post's Philip Rucker contributed to this report.