Former Director of National Intelligence James Clapper said on Thursday that Russia is preparing "the battlefield" to interfere with the 2018 midterm elections

"They are going to stretch the envelope as far as they can to collect information and I think largely if I can use the military phrase, prep the battlefield for 2018 elections," Clapper said on CNN.

Also on Thursday, CNN published a report citing current and former U.S. officials, that said Russia is ramping up its spying efforts against the U.S.

Clapper's comments came before the start of the G-20 summit in Hamburg, Germany, where President Trump plans to meet with Russian President Vladimir Putin on Friday. Republicans and Democrats have urged Trump to discuss the 2016 election interference by the Russians at the meeting.

"I think they are here to reconnoiter and collect as much as they possibly can on the United States who they consider as their prime adversary," Clapper said.