The Trump administration on Thursday took its strongest action to date to punish Moscow for interfering in the 2016 election, imposing fresh financial sanctions on Russian government hackers and spy agencies.

The administration also formally backed Britain’s claims that Moscow is almost certainly to blame for a chemical toxin attack against a former Russian spy living in England who was found comatose along with his daughter earlier this month.

The sanctions were the first such actions taken under legislation passed nearly unanimously last year by Congress and follow months of criticism that the White House has been slow to counter Russian aggression. But the steps taken Thursday fell well short of the full penalties Congress authorized and focused on a narrow list of targets rather than the broader range of individuals and entities believed to have played a role in Russia’s efforts to interfere in the election.

The Trump administration announced sanctions against Russian government hackers, spy agencies and trolls over malicious cyberattacks on March 15. (Reuters)

In both cases, pressure from Congress and allies helped nudge the White House toward a stronger response. Republicans have joined Democrats in urging the administration to penalize Russia more strongly, while suggesting that President Trump set aside concerns about examining the election interference that he initially dismissed as a “hoax.”

Lawmakers have been telling the White House for months that Russia will surely try to expand its interference in the upcoming congressional midterm elections.

Sen. Robert Menendez (D-N.J.), the senior Democrat on the Senate Foreign Relations Committee, called the sanctions announcement a “long overdue response” but noted that the administration has failed to implement six other mandatory provisions of the law enacted last year, including penalties affecting Russian defense and other industries.

In 1992, two Russian scientists approached The Post’s Will Englund, then the Moscow correspondent for the Baltimore Sun, with news of a secret nerve agent. (Joyce Lee, Will Englund/The Washington Post)

“I expect to see additional sanctions in short order against specific Russian entities responsible for undermining our democracy,” he said in a statement. “The longer we wait, we know the Russian government will continue to shift resources to other propaganda factories that spew disinformation and lies.”

Menendez also said the Obama administration had already sanctioned many of those on the Trump administration’s list. The White House also faced criticism that it muddied its response to the election interference by saying the penalties were also in response to Russia’s cyberattack last year against Ukraine and other countries, which officials have characterized as “the most destructive and costly” in history.

White House press secretary Sarah Huckabee Sanders would not say Thursday whether the administration considers Russia a friend or foe, instead turning the onus on Moscow.

“Russia’s going to have to make that determination. They’re going to have to decide whether or not they want to be a good actor or a bad actor,” Sanders said. “I think you can see from the actions that we’ve taken up until this point, we’re going to be tough on Russia until they decide to change their behavior.”

The penalties on 19 Russians were expected after a top administration official had pledged, under critical congressional questioning last week, that the administration would act within a week to use the mandate Congress had approved last summer.

The penalties also partly mirror the investigation pursued by special counsel Robert S. Mueller III. Thursday’s list included 13 people who had been indicted by Mueller, meaning they were already subject to legal jeopardy that is more serious than the sanctions.

A senior administration official said the timing of Thursday’s announcements were due to the completion of months of work to prepare the sanctions and the collective desire among the United States and allies to respond quickly to the “atrocious hostile act” against the former spy in England.

Separately on Thursday, the Department of Homeland Security and the FBI issued a report describing sophisticated Russian government attempts to target American and European power plants, nuclear facilities, airports and other critical infrastructure for cyberattacks.

It characterized the activity as “a multi-stage intrusion campaign by Russian government cyber actors,” while describing in minute detail how the digital assailants “staged malware, conducted spear phishing, and gained remote access into energy sector networks.”

The report indicated that the attackers appear to have penetrated the networks of key industrial sites in the United States and Europe, suggesting they could shut down or disrupt those systems with relative ease.

It repeated the key findings shared by the agencies in July, when they said that there was no evidence the hackers penetrated or damaged the core systems that control operations at the infrastructure sites and that public safety was never in jeopardy.

While the administration joined Britain and other allies Thursday in condemning Russia for the attack in Salisbury, England, that left the former spy and his daughter comatose, it has not said whether it plans any retaliation against Moscow. Britain has expelled Russian diplomats in protest.

After days in which the administration had not fully affixed blame over the incident, U.N. Ambassador Nikki Haley blasted Russia during a Security Council session Wednesday. Her remarks were approved by White House officials but went further than other officials had gone at that point.

“The United States believes that Russia is responsible for the attack on two people in the United Kingdom using a military-grade nerve agent,” Haley said, accusing Russia of violating international law.

“If we don’t take immediate concrete measures to address this now, Salisbury will not be the last place we see chemical weapons used,” Haley said. “They could be used here in New York or in cities of any country that sits on this council.”

Haley has been among the administration’s toughest voices about Russia, especially over its actions in support of Syrian President Bashar al-Assad, but her criticism rarely seemed part of a concerted administration policy to address what Secretary of State Rex Tillerson said was a deliberate Russian effort to expand its influence at U.S. expense.

Sanders also issued a pointed statement Wednesday that endorsed Britain’s expulsion of Russian diplomats.

“This latest action by Russia fits into a pattern of behavior in which Russia disregards the international rules-based order, undermines the sovereignty and security of countries worldwide, and attempts to subvert and discredit Western democratic institutions and processes,” Sanders said in one of the administration’s most comprehensive critiques to date. “The United States is working together with our allies and partners to ensure that this kind of abhorrent attack does not happen again.”

The United States and two major European allies on Thursday called the toxin attack the “first offensive use of a nerve agent” in Europe since World War II.

The joint statement from the leaders of France, Germany, the United States and Britain signaled a further ratcheting of international pressure on Russia that has been mounting since former double agent Sergei Skripal and his daughter, Yulia, were found comatose on March 4.

In the statement, the four leaders said they shared the view of British investigators that “there is no plausible alternative explanation” for the attack. They added that “Russia’s failure to address the legitimate request by the U.K. government further underlines its responsibility.”

Trump had said at the outset of his administration that he wanted to improve the disastrous U.S. relationship with Russia that he inherited from the Obama administration, a foreign policy goal that could help the United States achieve its own objectives in the Middle East and elsewhere.

Russia’s role in the election quickly overshadowed the relationship. Trump claims there was never any collusion between Moscow and his campaign, but critics say his anger over what he has called a “witch hunt” has colored the administration’s larger approach to Russia.

Max Bergmann, a former Obama administration official who heads the investigative Moscow Project at the Center for American Progress, called Thursday’s sanctions “a baby step” that does not suggest the administration intends to use much of the authority it has to go after Russian interference.

“Actually, this is not even a baby step,” Bergmann amended. “This is a mirage to make it look like they have implemented sanctions.”

Rep. Jim Banks (R-Ind.) commended the sanctions announcement, but like other lawmakers he urged the administration to go further.

“Russia’s continued attempts to undermine international order and to create destabilizing conditions must fail,” Banks said. “I will continue to support the robust use of all elements of U.S. national power to counter Russian aggression.”

Nick Miroff contributed to this report.