The issue focused on the fact that the US was not willing to share intelligence information with Russia.

"It's not a secret that Russia has been hacking the Democratic National Committee and other Democratic entities," Clapper said.

"It's just that they are not sharing it with us."

He added: "That is what we're working on."

Clapper went on to say the Russian hacking campaign may have involved "active measures" or "spying".

'No evidence'