Twitter said on Thursday it had suspended about 200 Russian-linked accounts as it probes online efforts to meddle with the 2016 US election, but an influential Democratic senator slammed its steps as insufficient.
Senator Mark Warner, the top Democrat on the Senate Intelligence Committee, summoned Twitter officials to testify behind closed doors on Thursday as part of broad investigation of Russian influence in the 2016 presidential election. Facebook faced a similar grilling earlier this month.
Lawmakers in both parties suspect social networks may have played a big role in Moscow's attempts to spread propaganda, sow political discord in the United States and help elect President Donald Trump. Moscow denies any such activity, and Trump has denied any collusion.
Twitter also briefed the House of Representatives Intelligence Committee on Thursday.
Warner said Twitter officials had not answered many questions about Russian use of the platform and that it was still subject to foreign manipulation.
The company's presentation to the Intelligence Committee "showed an enormous lack of understanding from the Twitter team of how serious this issue is," Warner said. He took particular umbrage at what he said was Twitter's decision to largely confine its review to accounts linked to fake profiles already spotted by Facebook.
Twitter said it had identified and removed 22 accounts directly linked to about 500 fake Facebook pages or profiles tied to Russia and that it unearthed an additional 179 accounts that were otherwise related.
Twitter declined to comment when asked about Warner's comments.
In addition to the private testimony by its officials, the company published a public blog post Thursday with its most detailed discussion to date of the steps it was taking to combat propaganda.
Warner in remarks to reporters called Twitter's statements "deeply disappointing" and "inadequate on almost every level."
The comments signalled that the congressional investigations into Russia's use of social media platforms would not ease up. Twitter, Facebook and other Internet companies including Alphabet Inc's Google are facing a steady stream of criticism as more information emerges about manipulation of their platforms during the 2016 election campaign.
Users, lawmakers and technology analysts have long criticised Twitter as too lax in policing fake or abusive accounts. Unlike Facebook, Twitter allows both anonymous accounts and automated accounts, or bots, making it far more difficult to police the service.
On Thursday, researchers at Oxford University published a study concluding that Twitter bots disseminated misinformation and propaganda at a higher rate in US battleground states than in noncompetitive states during a 10-day period around Election Day in November.