has continued to allow a Russian government-supported news network to advertise on its platform, even though the tech company sounded alarms about its ads to lawmakers investigating the Kremlin's interference in the 2016 presidential election.

In a meeting with House and Senate investigators last week, Twitter executives shared more than 1,800 promoted tweets from Russia Today, known as RT, and its three main accounts on the site. Some of the ads, valued in total at about $274,000, sought to promote RT's own stories, including those that sharply attacked Democratic presidential candidate Hillary Clinton.

Twitter's decision to share that information with Congress followed a report by the U.S. government's top intelligence agencies, which slammed RT in January as the "Kremlin's principal international propaganda outlet." Despite those concerns, though, the news network's three Twitter accounts -- @RT_com, @RT_America and @ActualidadRT — remain fully operational. And Twitter has not banned RT from advertising, according to a source familiar with the matter.

A spokeswoman for Twitter did not immediately respond to a request for comment.

, meanwhile, similarly has not shut down RT's official pages, one of which boasts more than 4.5 million followers. Nor has Facebook targeted any new advertising restrictions against the news network, a spokesman for the social giant told Recode, before adding they are monitoring the situation. Facebook nonetheless finds itself in congressional crosshairs for Russian-sponsored misinformation circulated in posts and advertisements before Election Day.

is still reviewing its platform for potential Russian interference. So far, it has not yet announced any findings or steps to harden its review process, and a spokeswoman declined to comment for this story. But RT videos had been viewed about 800 million times on Google-owned YouTube between the video platform's founding in 2005 and the U.S. government's January 2017 analysis of the election.

In many ways, though, Twitter's actions serve to illustrate the biggest dilemma facing the whole of Silicon Valley in combating misinformation spread by Russia or other malefactors online. Like many social networks, Twitter's service is global in nature, so any attempt to battle back sources or ideas — even those that frustrate U.S. users and regulators alike — could be seen as censorship here or elsewhere.

Last week, RT sharply criticized Twitter for even turning over copies of its advertisements to lawmakers on Capitol Hill. In a snarky-worded statement, the publication's editor in chief, Margarita Simonyan, stressed that "similar campaigns are conducted by the American media in the Russian segment of Twitter," before adding: "It'll be very interesting to find out how much they spend on it, who they target and for what purpose."

A spokesperson for RT did not immediately respond to a request for comment.

For Twitter and its peers, they could face further questions about its handling of RT and other Russia-tied accounts in a matter of weeks. The company has been invited along with Facebook and Google to testify in front of the House and Senate Intelligence Committees, which are set to hold hearings on the 2016 election in October and November, respectively.

Entering that hearing, Facebook has revealed that 470 accounts with connections to the Kremlin purchased about 3,000 ads, some of which sought to stoke political discord around controversial issues like race, religion and gun control. Those ads have been turned over to congressional investigators as well as Robert Mueller, the former FBI director who's leading an independent probe into the 2016 election.

Some of those same suspicious accounts on Facebook, however, also have ties to another 200 accounts on Twitter, a realization it shared with congressional investigators last week. But Twitter — as it turned over information about those users as well as RT's ads — quickly drew the ire of lawmakers like Sen. Mark Warner and Rep. Adam Schiff, who charged that the company should have looked more exhaustively at its records to determine the extent of Russian meddling.

Twitter, for its part, stressed it already has in place "stricter policies for advertising campaigns on Twitter than we do for organic content."

"We also have existing specific policies and review mechanisms for campaign ads, but will examine them with an eye to improving them," the company continued in its blog post last week. "We welcome the opportunity to work with the FEC and leaders in Congress to review and strengthen guidelines for political advertising on social media."

For its part, the U.S. government's own 2017 report on the election repeatedly slammed RT as the "Kremlin's principal international propaganda outlet." The news network had partnered with Wikileaks, for example, which had published hacked emails from the Clinton campaign, potentially with official Russian support, according to the Director of National Intelligence's findings. And RT ran a number of negative, accusatory stories about Clinton personally, at one point suggesting she and ISIS were funded by the same sources.

—By Tony Romm, Recode.net.

CNBC's parent NBCUniversal is an investor in Recode's parent Vox, and the companies have a content-sharing arrangement.

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