Facebook officials reported that they traced the ad sales, totaling $100,000, to a Russian “troll farm” with a history of pushing pro-Kremlin propaganda, these people said.

A small portion of the ads, which began in the summer of 2015, directly named Republican nominee Donald Trump and Democrat Hillary Clinton, the people said. Most of the ads focused on pumping politically divisive issues such as gun rights and immigration fears, as well as gay rights and racial discrimination.

The acknowledgment by Facebook comes as congressional investigators and special counsel Robert Mueller are probing Russian interference in the U.S. election, including allegations that the Kremlin may have coordinated with the Trump campaign.