Joe Biden tells Donald Trump to 'grow up' over hacking report

US Vice President Joe Biden has told Donald Trump to "grow up" as he criticised his "absolutely mindless" attacks on intelligence agencies.

Mr Biden was speaking after Mr Trump cast more doubt on allegations Russia meddled in the presidential election.

Mr Trump's remarks in a series of tweets come before he is due to be briefed on a report by intelligence agencies about the hacking allegations on Friday.

An unclassified version of the report will be made public next week. 

Already downplaying the report, Mr Trump questioned why the FBI was denied access to certain computer servers.

"The Democratic National Committee would not allow the FBI to study or see its computer info after it was supposedly hacked by Russia......," he tweeted.

"So how and why are they so sure about hacking if they never even requested an examination of the computer servers? What is going on?"

Mr Biden hit out at Mr Trump for failing to acknowledge the expertise of the intelligence community.  

"For a president not to have confidence in, not to be prepared to listen to, the myriad intelligence agencies, from defence intelligence to the CIA, is absolutely mindless," he said in an interview with the PBS network.

"The idea that you may know more than the intelligence community knows - it's like saying I know more about physics than my professor.

"I didn't read the book, I just know I know more."

Mr Biden added: "Grow up Donald, grow up, time to be an adult, you're president.

"Time to do something. Show us what you have."

He went on to call Mr Trump "a good man".

Director of national intelligence James Clapper earlier said he was confident that Russia hacked Democratic Party emails.

He said Russia - acting on orders from Vladimir Putin - helped spread propaganda and fake news to help Mr Trump's victory.

"We assess that only Russia's senior-most officials could have authorised the recent election-focused data thefts and disclosures," Mr Clapper said.

Mr Clapper claimed Russia has a "long history" of interfering in elections going back to the 1960s.

But he said they had never been as "aggressive" and "direct" as this time and pointed to a "highly advanced offensive cyber programme". 

Asked by a congressman on the Senate Armed Services Committee if they "will ascribe a motivation to Putin", Mr Clapper said: "Yes".

Committee chairman Senator John McCain said "every American should be alarmed" by Russia's meddling.

But he said the committee's probe did not intend to question the result of November's election.

The alleged hacking led to new sanctions by President Barack Obama against Moscow and 35 Russian diplomats were expelled from the US.

Moscow has denied the hacking allegations and dismissed the sanctions as an attempt to "harm Russian-American ties."