Putin has been repeatedly thrust into the campaign for the November 8 US election. Trump has praised him as a stronger leader than US President Barack Obama, drawing criticism from Clinton and some Republicans that he is too cozy with the Russian president. Trump has also refused to concede that Russia was behind the hacking of Democratic Party emails.

During Wednesday's presidential debate, Trump said he did not know Putin but would likely get along better with the Russian leader than Clinton, a former secretary of state.

"He said nice things about me," Trump said. "He has no respect for her, he has no respect for our president and I'll tell you what, we're in very serious trouble."

Clinton responded: "Well that's because he'd rather have a puppet as president of the United States."

"No, you're the puppet," Trump retorted, adding Clinton disliked Putin because he "has outsmarted her at every step of the way."

Earlier this week, Trump suggested that if elected, his first meeting with a foreign leader would be with Putin.

US-Russian relations have deteriorated in recent years over Moscow's intervention in the Syrian conflict, its annexation of the Crimean region from Ukraine and concerns about cyber attacks.

Director of National Intelligence James Clapper, who oversees 17 US intelligence agencies, has suggested that recent computer hacks targeting the Democratic Party were perpetrated by Russians, and predicted that cyber attacks would be a pressing challenge for the next president.

Putin said on Sunday that Russia did not seek confrontation with the United States and was not trying to influence the US election.