US presidential campaigns and related organisations have been targeted by hackers, the office of the US National Intelligence Director James Clapper says.
"We're aware that campaigns and related organisations and individuals are targeted by actors with a variety of motivations, from philosophical differences to espionage, and capabilities, from defacements to intrusions," Mr Clapper's spokesman Brian Hale said in a statement on Wednesday, deferring to the FBI for details on specific incidents.
Earlier, Mr Clapper said the US intelligence community had "already had some indications" of hacking attempts against presidential campaigns.
"As the campaign intensifies we'll probably have more" attacks, Mr Clapper said at a morning event at the Bipartisan Policy Center in Washington.
The last two US presidential cycles in 2008 and 2012 witnessed a barrage of cyber attacks from a range of adversaries targeting President Barack Obama's campaign and the campaigns of his Republican foes.
US intelligence officials have said many of the previous assaults were linked to Chinese hackers.