WASHINGTON (Reuters) - Despite public promises of cooperation from Facebook and other social media companies, congressional investigators are battling over how much data the companies should hand over to them on Russian efforts to influence the 2016 U.S. presidential election. Congressional sources said this week that Facebook Inc (FB.O) has been slow to cooperate. The company and others have said they are turning over information, but also that they are legally obligated to protect their users’ privacy. On visits to Capitol Hill on Wednesday and Thursday, Sheryl Sandberg, Facebook’s chief operating officer, met with leaders of the House Intelligence Committee and said the company wanted to help investigators and would turn over more information. “Things happened on our platform that shouldn’t have happened” in the lead-up to the election, Sandberg told the Axios website on Thursday. So far, however, the congressional sources said investigators have found it hard to extract all the relevant information from Silicon Valley about alleged Russian activity. But the committees have so far seen no need to issue subpoenas for the data, the sources added. Facebook and other major internet companies including Alphabet Inc’s Google (GOOGL.O) and Twitter Inc (TWTR.N) have faced a stream of recent revelations about how Moscow sought to use their platforms to sow discord in the United States and influence the election in favor of the Republican White House candidate, Donald Trump. Facebook disclosed last month that it had found some 3,000 politically divisive advertisements believed to have been bought by Russia before and after the presidential campaign.  The company has now shared with congressional investigators the ads, information on how they were paid for, and how they were targeted, a Facebook spokesman said. Sandberg told congressional investigators on Thursday that in addition to the ads, the company would provide the rest of the information from accounts linked to Russia, the spokesman said.     The sources said investigators were also pressing Twitter, Google and other companies for similar data, and urging Twitter to conduct a more comprehensive search of its data banks. “We have a set of strict ads policies including limits on political ad targeting and prohibitions on targeting based on race and religion,” a Google spokeswoman said, asked about the issue. “We are taking a deeper look to investigate attempts to abuse our systems, working with researchers and other companies, and will provide assistance to ongoing inquiries.”  A Twitter spokesperson did not respond to an email requesting comment. “Twitter has likely not released all potentially relevant data to congressional investigators in part because of their policy requiring a court order and their track record of defending user privacy by fighting such requests,” Adam Sharp, former head of news and government at Twitter, said in an interview. Twitter engineers are trying to regenerate some of the lost data, and may be able to retrieve some of it, said a person familiar with the company’s technology. The use of social media platforms was part of what U.S. intelligence agencies have concluded was a broader Russian effort to meddle in the election campaign, an allegation the Kremlin has denied. Several congressional committees, as well as special counsel Robert Mueller, are investigating Russian interference, including any potential collusion between Trump associates and Moscow. Trump has denied any such collusion. In September, Facebook disclosed that it had evidence that an operation based in Russia had spent $100,000 on thousands of sponsored posts promoting divisive social and political messages in a two-year period through May 2017. Facebook said it believed the messages were likely bought by people in Russia before and after the 2016 election.     Sources familiar with Facebook’s contacts with Congress said that as recently as July this year, company officials were denying the existence of any paid Russian messaging, and only later acknowledged that the company had found $100,000 in sponsored traffic linked to 478 Facebook accounts.       The sources said investigators think the paid messaging was generated by a group called the Internet Research Agency in St. Petersburg. U.S. officials have called it a “troll factory” that creates false identities or copies real ones to spread real, skewed, and fake information for the Kremlin. Congressional sources said some of the Facebook messaging went to groups with seemingly legitimate names such as Heart of Texas, Defend the Second, and United Muslims of America, which they said all had as many as 250,000 followers. These groups now appear to have been bogus, or set up to look like legitimate political organizations, and investigators want to learn more about the groups, their followers, and their origins, the sources said. They said Facebook lawyers have argued that turning over additional data could compromise its promise of privacy to its users. However, congressional investigators say that if Russian messengers used fake identities, they would have no legal claims to privacy. 
U.S. Congress tangles with Facebook, other social media firms over Russia probe