A dozen Russian intelligence officers have been indicted by a US grand jury for interfering in the 2016 presidential election.

The charges come just three days before US President Donald Trump is scheduled to meet Russian leader Vladimir Putin.

Announced by Deputy Attorney General Rod Rosenstein, 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.

Mr Rosenstein told reporters the Russian military officers were accused of "conspiring to interfere with the 2016 presidential election," including by hacking Democratic Party emails ahead of the vote.

"Eleven of the defendants are charged with conspiring to hack into computers, steal documents, and release those documents with the intent to interfere in the election," he said.

"One of those defendants and a 12th Russian are charged with conspiring to infiltrate computers of organisations involved in administering elections."

Mr Rosenstein said he had briefed Mr Trump about the indictment before today's announcement and that there was no allegation that US citizens were involved in the alleged crimes.

Mr Trump, who is currently visiting Britain, is scheduled to meet Mr Putin in Helsinki on Monday.

Russia's foreign ministry has said there was no evidence the 12 people indicted were linked to military intelligence or hacking into the computer networks of the US Democratic party.

The Russian ministry said the indictment was meant to damage the atmosphere before the summit between the Russian President Vladimir Putin and US President Donald Trump.

The US Justice Department said that officers of Russia's military intelligence agency, the GRU, "in their official capacities engaged in a sustained effort to hack into the computer networks of the Democratic Congressional Campaign Committee, the Democratic National Committee and the presidential campaign of Hillary Clinton and released that information on the internet under the names DC Leaks and Gufficer 2.0".

Mr Mueller, appointed by the Justice Department in May 2017 to take over an investigation earlier handled by the FBI, is investigating whether Mr Trump's campaign colluded with Russia and whether the president has unlawfully sought to obstruct the Russia investigation.

Mr Mueller has secured indictments against several former Trump campaign aides, including campaign chairman Paul Manafort, and former White House national security advisor Michael Flynn.

In February, Mr Mueller charged 13 Russians and three Russian companies in an elaborate conspiracy to interfere in the election.

The indictment said the Russians adopted false online personas to push divisive messages, travelled to the United States to collect intelligence and staged political rallies while posing as Americans. But that indictment had not directly tied the meddling effort to Russia's government.

US intelligence agencies have concluded that Russia used propaganda and hacking to meddle in the election in an effort to harm Mrs Clinton and eventually help Mr Trump.

A few hours before the indictments were announced, Mr Trump described the Mueller investigation as a "rigged witch hunt" that was hurting the US relationship with Russia.