Washington, Jan 7 (IANS): US President-elect Donald Trump has tweeted that "gross negligence" by the Democratic National Committee (DNC) allowed hackers to penetrate its servers.

"Gross negligence by the Democratic National Committee allowed hacking to take place," Trump tweeted on Friday. "The Republican National Committee had strong defence!"

The Obama administration officially blamed Russian authorities and President Vladimir Putin for repeated cyber attacks during the 2016 presidential campaign, declaring in a report that the Kremlin sought to "undermine" the US democratic process and "harm" Hillary Clinton's presidential candidacy, Politico reported.

"We assess Russian President Vladimir Putin ordered an influence campaign in 2016 aimed at the US presidential election," said the report, which is a declassified version of a longer, classified document the Central Intelligence Agency (CIA), Federal Bureau of Investigate (FBI) and National Security Agency (NSA) prepared at President Barack Obama's request, and which Trump was briefed on earlier Friday.

Trump's Friday tweet was posted shortly after Fox News host Sean Hannity decried "gross negligence" by the DNC in his show's opening monologue.