Twelve senior Russian intelligence officers have been charged with hacking into Democrat computers in a bid to sabotage the 2016 US presidential election.

The charges were brought as part of special counsel Robert Mueller's investigation into whether there was any collusion between Donald Trump's campaign and Russia.

It was also alleged that Russian agents stole information on 500,000 US voters after hacking a state US election board.

Deputy Attorney General Rod Rosenstein announced the charges at the US Department of Justice in Washington.

It comes days before Mr Trump's Helsinki meeting with Russian President Vladimir Putin, casting a major shadow over the encounter.

Mr Rosenstein said he had briefed Mr Trump ahead of time about the development in recent days.

He said: "I briefed the president. It's important for the president to know what evidence we have of foreign interference."

He said agents had acted "without reference to politics" and there was "evidence to justify the charges".