WASHINGTON (AP) — Senators are ripping Facebook, Twitter and Google for missing signs that advertisers with ties to Russia were exploiting their services to sway last year's presidential election.

Minnesota Democrat Al Franken was especially outraged as he questioned Facebook's top lawyer Tuesday during a Senate subcommittee hearing into Russia's interference in the 2016 election. He demanded to know why Facebook couldn't figure out how an ad paid for in rubles had been purchased by a Russian account.

Franken fumed: "How could you not connect those two dots?"

Colin Stretch, Facebook's general counsel, sheepishly admitted the company missed a key signal and should have had a "broader lens." But he wouldn't commit to banning U.S. political ads purchased in foreign currencies.

Facebook's top lawyer says technical limitations prevented the online social network from determining if deceptive ads aimed at influencing last year's U.S. presidential election may have been purchased by other foreign adversaries besides Russia.

Colin Stretch, Facebook's general counsel, has told a Senate subcommittee that the company didn't have any evidence that accounts linked to China or North Korea had bought politically charged ads.

But he stopped short of saying with certainty that other countries hadn't purchased misleading or false ads on Facebook. About 5 million advertisers buy space on the site each month.

Facebook detected that Russian-linked accounts bought thousands of political ads on its service after questions began to mount this year about whether Russia helped get President Donald Trump elected.