Former US FBI director James Comey said that social media companies needed to “worry” about foreign political propaganda on their networks, but he had few ideas on how to counter it.

In an interview with Reuters, Comey also said he would be leery of the Federal Bureau of Investigation trying to track propaganda in the US, let alone take action against it, while acknowledging that it was a major problem for the US political system.

“I don’t have a great answer for them,” Comey said of social media companies including Facebook and Twitter, which were major venues for what US intelligence agencies have said was a Russian-sponsored effort to help President Donald Trump win the 2016 US election.

Comey’s comments followed former director of National Intelligence James Clapper’s conclusion in a new book that the Russian election meddling, which allegedly included illegal hacking and leaking of stolen information as well as propaganda, had a decisive influence in electing Trump.

Trump fired Comey as the FBI investigated the Russian election interference, setting the stage for the appointment of Special Counsel Robert Mueller and his wide-ranging enquiries.

Comey has been criticised for the FBI’s failure to counter Russia’s election meddling while it was happening.

But Comey said the FBI should not get involved in fighting propaganda because it is a “rule-bound institution”, with strict policies that serve as an appropriate check on its power.

“You’d want to be very thoughtful about having the FBI, without having a predicated investigation, be monitoring speech in the US, because it’s often very difficult to tell, is it coming from a nation state?” Comey said. “So in theory that might involve collecting more broadly on speech in the US.”

He said those same concerns had kept the FBI from tracking an influence campaign that included Russian-driven Facebook posts that reached more than 100 million people on that social network alone ahead of the 2016 election.

Comey avoided answering questions about the ongoing Mueller probe and his own role in the earlier version of the investigation, but he scoffed at Trump’s accusation last week that the FBI had planted a spy inside his 2016 campaign.

Comey said he could not comment directly on the claim, floated last week by Trump and Republican supporters in Congress.

Sign up to our free newsletters

Get the best updates straight to your inbox:
Please select at least one mailing list.

You can unsubscribe at any time by clicking the link in the footer of our emails. We use Mailchimp as our marketing platform. By subscribing, you acknowledge that your information will be transferred to Mailchimp for processing.