By Agence France-Presse
The charges were drawn up by Special Counsel Robert Mueller, the former FBI director who is looking into Russian interference in the November 2016 vote and whether any members of Trump's campaign team colluded with Moscow.
Democratic leaders immediately called for Trump to cancel Monday's scheduled meeting with Putin in Helsinki, but the White House said the summit would go ahead.
"It's on," spokeswoman Sarah Sanders said.
The 29-page indictment accuses members of the Russian military intelligence agency known as the GRU of carrying out "large-scale cyber operations" to steal Clinton campaign and Democratic Party documents and emails.
"There's no allegation that the conspiracy changed the vote count or affected any election result," Deputy Attorney General Rod Rosenstein said in announcing the charges at a press conference in Washington.
"There's no allegation in this indictment that any American citizen committed a crime," Rosenstein added, although the "conspirators corresponded with several Americans during the course of the conspiracy through the internet."
However, he said, "there's no allegation in this indictment that the Americans knew they were corresponding with Russian intelligence officers."
Rosenstein said he briefed Trump about the indictment before Friday's announcement and that the timing was determined by "the facts, the evidence, and the law."
News of the indictment came as Trump was meeting Queen Elizabeth II and just 72 hours before his meeting with Putin.
"This indictment makes clear just how vast this operation was -- including Russian intelligence officers' intrusion into the website of a state election board and theft of information related to approximately 500,000 voters," Democratic National Committee (DNC) chair Tom Perez tweeted.
"The Russian government attacked our democracy in 2016, and the DNC was a primary target of that attack," he wrote.
Calls to cancel Putin meeting
Senator Chuck Schumer, the Democratic Senate minority leader, urged Trump to cancel the Putin talks.
"These indictments are further proof of what everyone but the president seems to understand: President Putin is an adversary who interfered in our elections to help President Trump win," Schumer said in a statement.
"President Trump should cancel his meeting with Vladimir Putin until Russia takes demonstrable and transparent steps to prove that they won't interfere in future elections."
Republican Senator John McCain said the summit should be called off if Trump is not ready to warn Putin there is a "serious price to pay for his ongoing aggression towards the United States and democracies around the world."
"If President Trump is not prepared to hold Putin accountable, the summit in Helsinki should not move forward," McCain said.
Speaking in Britain before the indictments were unveiled, Trump said he would ask Putin about the allegations of election meddling.
"I will absolutely, firmly ask the question, and hopefully we'll have a good relationship with Russia," he told a joint press conference with British Prime Minister Theresa May.
But he simultaneously denounced the Mueller investigation as a "rigged witch hunt," and said he has been "tougher on Russia than anybody."
The US president recalled that 60 intelligence officers were expelled from the Russian embassy in Washington in response to a nerve agent attack on a former Russian spy in Britain.
Russia has denied any involvement in the attack and rejected accusations that it interfered in the US presidential election in a bid to help Trump win.
- No 'knowing involvement' by Team Trump -
In a statement, the White House highlighted Rosenstein's remarks that no Americans had been charged.
"Today's charges include no allegations of knowing involvement by anyone on the campaign and no allegations that the alleged hacking affected the election result," it said. "This is consistent with what we have been saying all along."
Trump's lawyer, Rudy Giuliani, said on Twitter that the indictments were "good news for all Americans."
"The Russians are nailed. No Americans are involved. Time for Mueller to end this pursuit of the President and say President Trump is completely innocent," Giuliani said.
Rosenstein called for unity in the face of Russian meddling.
"When we confront foreign interference in American elections, it is important for us to avoid thinking politically as Republicans or Democrats and instead to think patriotically as Americans," he said.
The indictment alleges that beginning in March 2016, the GRU agents began targeting over 300 employees and volunteers of the Clinton campaign, the Democratic Congressional Campaign Committee (DCCC) and the DNC.
"The conspirators covertly monitored the computers of dozens of DCCC and DNC employees, implanted hundreds of files containing malicious computer code, and stole emails and other documents," it said.
Around June 2016, they began releasing tens of thousands of the stolen emails and documents using "fictitious online personas, including 'DCLeaks' and 'Guccifer 2.0,'" the indictment said.
Some of the documents and emails were released through a website identified in the indictment only as "Organization 1" -- believed to be Julian Assange's WikiLeaks.
Other documents and emails were made public through a website and Twitter account known as DCLeaks, which the GRU falsely attributed to a group of "American hacktivists."
Mueller previously indicted 13 Russians and three companies for allegedly interfering in the presidential vote.
Former Trump campaign chairman Paul Manafort has been charged with money laundering and other crimes, while former national security adviser Michael Flynn has admitted lying to the FBI.