https://www.washingtonpost.com/news/the-switch/wp/2017/10/26/twitter-bans-russian-government-news-sites-rt-and-sputnik-from-buying-ads/

Twitter said its decision to block advertising from the sites stemmed from the conclusion of the U.S. national intelligence report in January that said that the Kremlin used the sites to interfere in the 2016 U.S. presidential election.