Some of the Facebook ads linked to a Russian effort to disrupt the American political process and stir up tensions around divisive social issues, released by members of the U.S. House Intelligence Committee. (Jon Elswick/AP)

Facebook is creating an online tool to allow users to determine if they might have been exposed to Russian disinformation during the 2016 presidential election and its fractious aftermath, the company announced Wednesday.

The new tool, which the company said will be available by the end of the year, is the latest move by Facebook to respond to public and political pressure to reveal the extent of the Russian disinformation campaign waged on its social media platform and on Instagram, which Facebook owns.

Together nearly 150 million Facebook and Instagram users may have had pieces of Russian disinformation content — both paid ads and free posts — reach their accounts, the company has said, though it also has said there is no way to know how many actually saw that content.

The new tool will be an online portal, available through Facebook's Help Center. It will allow users to see if pages or accounts they "liked" or followed between January 2015 and August 2017 were created by the Internet Research Agency, a St. Petersburg troll farm that Russian operatives used to pump out divisive content on race, religion, gun rights, immigration and other issues into the American online political conversation.

Some of the Russian pages and accounts explicitly called for the election of Republican Donald Trump or denigrated his Democratic opponent, Hillary Clinton, and some others called for real-world political rallies — many peopled heeded those calls by showing up at the time and places dictated by the Russian trolls.

"It is important that people understand how foreign actors tried to sow division and mistrust using Facebook before and after the 2016 US election," Facebook said in its announcement Wednesday. "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."

Several Democratic lawmakers — including Sens. Jack Reed (R.I.) and Richard Blumenthal (Conn.), as well as Rep. Teri Sewell (Ala.) — had pushed Facebook to find a way alert its users about their exposure to Russian disinformation. Blumenthal sent a letter calling on Facebook to find a way to alert its users, setting Wednesday as a deadline for the company to take action.

Sewell, a member of the House Intelligence Committee, asked Facebook's general counsel, Colin Stretch, in a hearing on Nov. 1 whether the company had "an obligation to notify" its users.

Stretch replied, "We have tried to notify people about the issue broadly through information on the website through our white paper last April and hard questions blog and working with the committee; we're open to all of this information being released publicly. It's a much more challenging issue to identify and notify reliably people who may have been exposed to this content on an individual basis."

Ellen Nakashima contributed to this report.