Facebook will show users if they followed or 'liked' Russia propaganda accounts on its service or on Instagram.

The company will launch a portal to let people see which accounts of the Internet Research Agency they followed between January 2015 and August 2017. The Internet Research Agency is the Russian firm that created thousands of incendiary posts from fake accounts posing as U.S. citizens.

The tool will be available by the end of the year.

"It is important that people understand how foreign actors tried to sow division and mistrust using Facebook before and after the 2016 US election. That's why as we have discovered information, we have continually come forward to share it publicly and have provided it to congressional investigators. And it's also why we're building the tool we are announcing today," Facebook said.

Facebook, Google and Twitter appeared in early November for hours of congressional testimony to explain how Russia used the platforms to manipulate U.S. citizens. The companies vowed to do more to prevent anything similar from occurring in the future, and said they would look into the possibility of informing users about their exposure.