Washington, April 5 (IANS): President Donald Trump's administration is expected to impose additional sanctions against Russia by Friday, according to US officials.

The sanctions are economic and designed to target oligarchs with ties to President Vladimir Putin, the officials told The Washington Post on Wednesday.

However, the final number of Russians facing punitive action remains fluid.

In recent weeks, Trump's national security advisers have pushed for more sanctions after the poisoning of Sergei Skripal, a former Russian spy in England, interference in the US 2016 elections and a cyber-attack described as the most destructive and costly in history.

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

McMaster's remark came hours after 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.

Last week, the US expelled 60 Russian spies and diplomats in response to the poisoning of Skripal and his daughter Yulia, the largest expulsion of Russians in American history, The Washington Post reported.

In early March, the administration also slapped fresh sanctions on Russian government hackers and spy agencies for interfering in the 2016 election and the cyber-attack.