Newly released documents show how Russian propagandists on Facebook grew increasingly sophisticated and inflammatory in their tactics over two years as they worked to sow discord in the U.S. before and after the 2016 presidential election.

Democrats on the House Intelligence Committee on Thursday made public for the first time the full cache of more than 3,000 ads that Facebook Inc. said were purchased by a pro-Kremlin group, the Internet Research Agency. The ads, fewer than 50 of which had previously been revealed, offer...