Democratic presidential candidate Hillary Clinton has expressed concern about "credible reports" of Russian interference in the US election and accused Donald Trump of being fixated on dictators including Russia's Vladimir Putin.
Taking questions from reporters for more than 20 minutes on her campaign plane, Clinton said both Democrats and Republicans should be concerned about Russia's behaviour.
"The fact that our intelligence professionals are now studying this and taking it seriously raises some grave questions about potential Russian interference with our electoral process," Clinton said.
"We are facing a very serious concern. We've never had a foreign adversarial power be already involved in our electoral process. We've never had the nominee of one of our major parties urging the Russians to hack more," she said.
Trump, the Republican nominee, has praised Putin, the president of Russia, and has called on Moscow to dig up tens of thousands of "missing" emails from Clinton's time as head of the US State Department. He later said his comments were meant to be sarcastic.
Clinton has previously tied Russian intelligence services to the cyber hack on the Democratic National Committee.
Asked on Monday if she believed the Russian government was trying to help elect her opponent, Clinton paused.
"I often quote a great saying that I learned from living in Arkansas for many years: If you find a turtle on a fencepost it didn't get there by itself," she said.
"I think it's quite intriguing that this activity has happened around the time Trump became the nominee."
Clinton, whose use of a private email account during her time as secretary of state has dogged her 2016 presidential campaign, said she understood and took classification seriously when she was President Barack Obama's top diplomat.
Clinton said that the attacks on her family's foundation were not rooted in fact and sidestepped a question on whether her daughter, Chelsea, should step down from the foundation's leadership if she is elected in November.