US President Donald Trump has criticised the administration of his predecessor Barack Obama over alleged Russian hacking to help him win the 2016 presidential election.

"Why didn't they do something about it?" he tweeted, adding that Mr Obama had been told about it before the vote.

It follows pressure on Mr Trump to cancel Monday's talks with Russia's Vladimir Putin following the indictment of 12 Russians on Friday.

Russia denies allegations of hacking.

Mr Trump is due to meet Mr Putin in the Finnish capital Helsinki.

However the hacking allegations have sparked a heated war of words between Washington and Moscow.

What are the allegations?

The 11-count indictment names the Russians defendants, alleging they began cyber-attacks in March 2016 on the email accounts of staff for Hillary Clinton's presidential campaign.

They are accused of using keystroke reading software to spy on the chair of the Democratic National Committee (DNC) and hack into the party's computers.

Mr Rosenstein said the conspirators used fictitious online personas, including "DCLeaks" and "Guccifer 2.0", to release thousands of stolen emails.

They are also accused of stealing the data of half a million voters from a state election board website.

Special Counsel Robert Mueller is investigating US intelligence findings that Russians conspired to sway the 2016 election in Mr Trump's favour.

As of Friday, the inquiry has indicted 32 people - mostly Russian nationals in absentia - as well as three companies and four former Trump advisers.

None of the charges allege Trump advisers colluded with Russia to interfere with the presidential campaign.

Former National Security Adviser Michael Flynn and George Papadopoulos, a former foreign policy adviser, have pleaded guilty to making false statements about their contacts with Russians.

Former Trump campaign chairman Paul Manafort and his deputy Rick Gates were charged with money laundering relating to their political consultancy work in Ukraine.