US presidential elections: Vladimir Putin himself involved in the hack, claims report

US intelligence officials now believe that Russian President Vladimir Putin was personally involved in hacking during the American election campaign as part of a vendetta against Hillary Clinton, a media report said on Thursday.

Putin personally instructed how material hacked from US Democrats was leaked and otherwise used, NBC News reported quoting two senior officials with access to this information.

The officials said they have a "high level of confidence" in this new assessment, NBC reported.

Asked if there was basis to the allegations, Putin's spokesman Dmitry Peskov told journalists: "Ridiculous nonsense cannot have any basis."

Last weekend The Washington Post reported a CIA evaluation that Russia had hacked the emails of US persons and institutions as a way to sway the election in favour of Republican Donald Trump, who eventually did beat Clinton on November 8.

Putin is said never to have forgiven Clinton — then secretary of state — for publicly questioning the integrity of parliamentary elections in 2011 in Russia, and accused her of encouraging street protests.

The intelligence officials told NBC that Putin's goals in the alleged hacking began as revenge against Clinton.

But they transformed into a broader effort to show that the world of US politics was corrupt and to, in the words of one official, "split off key American allies by creating the image that (other countries) couldn't depend on the US to be a credible global leader anymore."

In preparation for possible retaliation, US intelligence agencies have intensified probing of Putin's personal wealth, NBC said, citing US officials.

Trump, who has spoken warmly of Putin, has dismissed as "ridiculous" the allegation that Russia was behind the hacking of the Democratic National Committee and people close to Clinton.

Leading US lawmakers have called for a formal congressional investigation into the hacking.