U.S. Democratic presidential candidate Hillary Clinton said on Sunday that Russian intelligence services hacked into Democratic National Committee computers and she questioned Republican rival Donald Trump's overtures to Russian President Vladimir Putin.

"We know that Russian intelligence services hacked into the DNC and we know that they arranged for a lot of those emails to be released and we know that Donald Trump has shown a very troubling willingness to back up Putin, to support Putin," Clinton said in an interview with "Fox News Sunday."

The White House has declined to speculate on who was behind the hack of Democratic Party computers, referring to an ongoing investigation by the Federal Bureau of Investigation. Cybersecurity experts and U.S. officials, however, said they believed Russia engineered the release of the emails to influence the Nov. 8 U.S. presidential election.