Donald Trump takes issue with Hillary Clinton's criticism of Vladimir Putin

Republican US presidential nominee Donald Trump has criticised rival Hillary Clinton for being too tough on Russian President Vladimir Putin, once again raising eyebrows about the Republican candidate's relationship with Putin.

Speaking at a rally in Springfield, Ohio, as he kicked off a day-long swing through the battleground state, Trump, on Thursday, took issue with Clinton's criticism of the Russian leader, who has been denounced in the West for his military assertiveness and anti-democratic tendencies.

"She speaks very badly of Putin, and I don't think that's smart," Trump told a crowd of thousands, noting that Russia has nuclear weapons.

"How do you speak so badly of someone?" he asked.

Trump has been criticised throughout his campaign for failing to denounce Putin and repeatedly denying connections US intelligence officials say they've found between Russia and recent hacking efforts that appear aimed at influencing the outcome of November's election.

Trump has long argued that the US would be better off if it had a more productive working relationship with Russia and has called for the two countries to work together to take on Islamic State militants, despite their differences over Syrian President Bashar Assad's government.

Trump's running mate, Mike Pence, has taken a harder line on Putin, describing him during the vice presidential debate as a "small and bullying leader".

Trump has said that Putin is a stronger leader than President Barack Obama and praised him for exerting "strong control over his country".

The US has accused Russia of coordinating hacks on Clinton's campaign emails. But Putin on Thursday dismissed those claims, saying the allegations were designed to distract the public from real issues.

He said suggestions that Russia was trying to bolster Trump were "sheer nonsense".

"It's just an instrument of political struggle, a way of manipulating public opinion," he said in Sochi.

Still, the Russian leader added that while Trump may sound "extravagant", he was trying to reach out to people who are tired of elites. He said, "Time will tell how effective it is for him."