U.S. President Donald Trump has said China is interfering with the November midterm elections, but the findings of top cybersecurity firms are casting doubt on his claims.

"We haven't observed any evidence of Chinese targeting the midterms or anything that would be relevant to upcoming elections," said Luke McNamara, a principal intelligence analyst at the cybersecurity firm FireEye Inc., which works with some state and local authorities to monitor election threats.

Jon DiMaggio, a senior threat intelligence analyst at Symantec Corp., which studies threats to campaigns, candidates, states and on social media, said he has observed "no digital trail of bread crumbs that is leading back to China."