President Barack Obama sanctioned Russian officials and entities on Thursday in response to Moscow’s reported hacking during the U.S. presidential election.

“All Americans should be alarmed by Russia’s actions,” the president said in a statement.

In addition to hitting two Russian intelligence agencies, three companies and four individual intelligence officers with sanctions banning them from travel and business with U.S. companies or individuals, Obama ordered 35 Russian operatives posted at diplomatic facilities in Washington and San Francisco to leave. The president asked the State Department to bar Russians from entering two Russian-owned compounds in Maryland and New York that were used to gather intelligence, according to his statement. And Obama’s Treasury Department barred U.S. business with two Russians accused of cyber-theft of money and data.

Obama left the door open for further action, including a potential cyberattack on Russia. “We will continue to take a variety of actions at a time and place of our choosing, some of which will not be publicized,” he stated.

If Russia is not deterred now, the Obama administration believes it will continue to interfere in U.S. elections, as well as elections in U.S.-friendly countries, officials told reporters in a call. One official described Russian government actions against U.S. diplomats posted in Russia as part of the country’s “flagrant violation of diplomatic norms.”

Obama’s successor, president-elect Donald Trump, has cast doubt on the U.S. intelligence community’s pre-election declaration that Russia was responsible for unearthing and releasing Democratic National Committee communications damaging to Trump’s opponent, former Secretary of State Hillary Clinton.

Following Trump’s victory, leaks to The Washington Post revealed that many intelligence officials ― including the leaders of the FBI and the CIA ― believe Russian President Vladimir Putin authorized the hacks to aid Trump, who has previously praised the Russian leader. On Wednesday, Trump said it was time to “move on” and repeated that he believes it’s impossible to know who targeted Clinton.

In a statement Thursday, the president-elect said he would meet with intelligence officials next week to discuss the issue, but said he still wanted the matter to be left in the past.

“It’s time for our country to move on to bigger and better things,” Trump said Thursday.

But Obama appears committed to proving Russia’s responsibility despite the denials from Trump and the Kremlin. His administration wants Congress to receive intelligence reports that lay out the evidence before Trump enters office and is able to call off such investigations.

“I would never expect Russia to come out with their hands up and acknowledge they did it,” an official said on the Thursday call. “They still deny that they are intervening in eastern Ukraine.”

These data theft and disclosure activities could only have been directed by the highest levels of the Russian government ... Such activities have consequences. President Barack Obama

The Department of Homeland Security and the FBI tried to bolster their case to the public on Thursday by releasing a 13-page joint report providing some details of what the agencies know about the Russian actions.

The report cites “technical indicators” that the hacking was tied to Russian civilian and military intelligence services. It adds that in some cases, the Russian actors “masqueraded as third parties, hiding behind false online personas designed to cause the victim to misattribute the source of the attack.”

Actors “likely associated” with Russian civilian and military intelligence services “are continuing to engage in spearphishing campaigns,” and launched one attack “just days after the U.S. election,” the report stated.

The government also released a list of IP addresses associated with the alleged Russian activity, including addresses based in the U.S., Mexico, Puerto Rico, Germany, Vietnam, Canada, Thailand, South Korea, Spain, China, Denmark, the U.K., Luxembourg and Russia.

The report does not go into detail about how the U.S. determined that the Russian government was involved. But senior U.S. officials said there was “no debate” within the intelligence community that Russia interfered in the election. This wasn’t a “he-said-she-said” situation, one official said. Instead, the official added, there are facts, and then there’s what Russia said.

Officials said they plan to release another public report with more details on the findings before Obama leaves office.

The independent cybersecurity firm Crowdstrike has conducted its own analysis and concluded that the Russian military intelligence agency now under sanctions, the GRU, was behind the attack on the Democratic National Committee.

The Intercept reported Thursday morning that the National Security Agency has successfully tracked Russian hacking in the past; its capabilities may be the key to the intelligence community’s confidence in Russia’s meddling.

“These data theft and disclosure activities could only have been directed by the highest levels of the Russian government,” Obama said on Thursday. “Moreover, our diplomats have experienced an unacceptable level of harassment in Moscow by Russian security services and police over the last year. Such activities have consequences.”

Putin’s spokespeople attacked the Obama team in personal terms, calling them “losers” and promising retaliation.

REUTERS/Stevo Vasiljevic A billboard featuring pictures of U.S. President-elect Donald Trump and Russian President Vladimir Putin in Danilovgrad, Montenegro, on Nov. 16, 2016.

The president’s actions are occurring under executive order, so it is possible that Trump could undo them once he’s in office. But Obama’s team believes their framing of the issue would make such a step highly embarrassing for the new president.

“If a future president decided he wanted to allow in a large tranche of Russian intelligence agents, presumably a future president could do that,” an Obama aide said. “We don’t think it would make much sense to reopen Russian intelligence compounds ... we don’t think it makes much sense to invite back in Russian intelligence agents.”

Trump would also face strong political opposition if he attempted to soften Obama’s approach. Many on Capitol Hill, including Republicans, are keen to signal toughness against Moscow.

House Speaker Paul Ryan (R-Wis.) issued a statement commending Obama’s plan soon after the president announced it. “Russia does not share America’s interests. In fact, it has consistently sought to undermine them, sowing dangerous instability around the world,” he said, though he criticized the president’s past handling of Moscow.

Senate Majority Leader Mitch McConnell (R-Ky.) praised the move as well.

Democrats, including Senate Minority Leader Chuck Schumer (N.Y.) and House Intelligence Committee ranking member Adam Schiff (Calif.), praised the actions as well.

“We can never know if the Russian dirty tricks campaign was decisive in tipping the outcome of the presidential election, but make no mistake ― Putin’s real target was not the Clinton campaign or one political party, but our entire system of governance,” Schiff said.

German officials have been warning for months that Russia may interfere with its own elections, which will be held next year, and the Obama administration officials on Thursday’s call said they worried that U.S. allies are already in Moscow’s crosshairs.

Schiff suggested further sanctions may be necessary, echoing Republican Sens. John McCain (Ariz.) and Lindsey Graham (S.C.), who praised Obama’s actions Thursday and said they are looking at further punishments for Moscow.

The Trump transition team did not immediately respond to a request for comment. The White House informed them of the move earlier in the day, CBS reported.

Sam Levine contributed reporting.

This story has been updated with Mitch McConnell’s stance on the sanctions, as well as a statement from Vladimir Putin’s spokespeople and Trump’s Dec. 29 statement.