WASHINGTON -- The language was intended to stir up hate, using pictures and incendiary language: "They won't take over our country if we don't let them in."

The group behind the messages called itself Secured Borders. But investigators say it was part of a Russian campaign to influence the 2016 election, CBS News' Jeff Pegues reports.

To that end, Secured Borders used Facebook's event and initiation tool to promote an anti-immigrant rally in Twin Falls, Idaho, a city it called "a center of refugee resettlement" responsible for a "huge upsurge of violence toward American citizens."

That was false, and the rally itself never happened, in spite of the Russian campaign.

"They are using these new social media sites, which is kind of a wild, wild West with very few rules, to influence the election," said Sen. Mark Warner, the ranking Democrat on the Senate Intelligence Committee, which is investigating Russian interference in the 2016 presidential election.

"I think what we've seen so far from Facebook is only the tip of the iceberg," Warner said.

Facebook shut down Secured Borders, but there are other groups, including one that worked out of Texas. CBS News has learned that investigators believe there were many more, and are scrambling to identify them.

A source familiar with the investigation suggested that there are likely many more incidents of "Facebook fronts" for the Russians urging Americans to take action.

Just last week, Facebook disclosed that an internal investigation identified about 3,000 ads, costing $100,000, containing messages about divisive issues.Those ads also were linked to Russian internet trolls.

A Facebook official told CBS News that because of federal laws and the ongoing Russia investigations the company is limited in what it can say publicly. The company says it is still digging into how far and wide Russia's activities were using the social media giant's reach.

U.S. intelligence officials believe the Kremlin sought to interfere in the U.S. election, and one tactic of the multi-pronged attack was a wave of misinformation.

Sen. Mark Warner CBS News

Warner said the company hasn't been transparent enough and needs to step up its efforts.

"I think there's much more than 350-odd accounts that were involved in this process," Warner said, referring to ads linked to Russia that the company acknowledged last week. "I think it was much more than the simply one internet troll farm they found in St. Petersburg. And frankly, Facebook, who prides itself on knowing more about you and me than frankly the United States government knows, I got to believe they know more about this or could find more out about it if they put adequate resources behind it."

Warner said Facebook was "slow" to come out and reveal its findings, and that "they didn't check on other countries that were close to Russia."

"Moldova, for example, there were lots of indications that there were internet trolls working throughout the election out of that country and other countries in Eastern Europe," he said. "I don't believe they've run any of that information."

Warner said there are meetings now underway to discuss next steps but indicated a strong likelihood that he wants more from the social media giants.

"We will have Twitter in and then on a staff level, I want Facebook, Twitter and potentially other social media firms," he said. "I think they owe an explanation to all of us on the committee."

There are growing indications social media company executives will be called to testify in public on Capitol Hill.