San Francisco (CNN) FBI Director Christopher Wray said Tuesday that while the US had not seen a "material impact on election infrastructure" from foreign adversaries in the recent midterm elections, foreign influence campaigns pitting Americans against each other on social media have continued "virtually unabated."

Wray, speaking at the RSA cybersecurity conference in San Francisco, said the FBI has been working closely with the social media companies to counter the threat, and that the cooperation had been a "great example of how the government and private sector can work together in a common defense."

He said the wider cyber threats facing the United States are "unlike anything we have had in our lifetimes," citing an uptick in threats from Russia, Iran, China and North Korea.

Wray also said the US is seeing more "blended" attacks, where nation-states are partnering with cyber criminal gangs to attack the US.

He fingered China, saying that when he became director, "The thing that most shocked me was the breath and the depth and the scale of the Chinese counterintelligence threat."