Sen. Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee, said just “the tip of the iceberg” has been revealed about Russia’s use of targeted ads on Facebook to influence the 2016 presidential campaign.

In an interview with MSNBC’s Rachel Maddow on Wednesday, Warner said Facebook has more work to do investigating how Russians used the site to tamper with the election.

“I think that we’re still at the tip of the iceberg,” Warner said. “The fact is, I don’t think Facebook has put the resources, the time” into probing the matter. “I think there’s a lot more” for the company to do, he added.

Last week, Facebook said $100,000 was spent by an influence operation likely based in Russia on 3,000 ads featuring divisive political messages. The site said it has suspended 470 “inauthentic” accounts and pages promoted by the ads.

“My understanding is they didn’t even go back and check all those accounts to see if they had put out other ads,” Warner said, referring to what he called “troll farms” based in St. Petersburg that Facebook said it had discovered.

“We know from past reporting that there were a number of these troll and other efforts, internet-based efforts that came out of other countries in eastern Europe that Russia was known to organize,” Warner said. “We’ve not had any evidence [Facebook] investigated those efforts as well. So I think there’s a lot more questions.”

He compared the number of known fake accounts created to influence the U.S. election to the tens of thousands found during the French presidential election that took place earlier this year. The significantly fewer fake accounts so far discovered that focused on the U.S. vote means there’s more to investigate in the U.S.-based operation.

“To me it seems that the Russian intervention in the American election was extensive, coordinated and frankly unprecedented,” Warner said. “I’ve got to believe if they took that much on there’s probably more to be discovered.”