The 418 new accounts linked to Russia mimicked the behavior of the 3,843 accounts that were run by the I.R.A. Yoel Roth, Twitter’s head of site integrity, said in the blog post that the company could not prove that the new accounts it discovered were run by the I.R.A.

Though Twitter and Facebook announced their findings separately, the companies — both under pressure to crack down on disinformation on their services — collaborated on the investigation.

The most successful and ambitious of the disinformation efforts detailed on Thursday was believed to be an Iranian-led campaign that used Facebook and Twitter to reach millions of people across dozens of countries.

The Iranian campaign had sought to sway public discourse in countries across the Middle East, Europe and Asia, Twitter and Facebook said. Some of the social media accounts involved in the campaign had been active for over a decade. Facebook said it had removed 783 pages, groups and accounts with ties to Iran, while Twitter removed 2,617 Iranian-linked accounts.

Facebook’s investigation focused on pages tied to Iran that in some cases were nearly nine years old. The page administrators and account owners claimed they were local and posted items on topics like Israeli-Palestinian relations and the conflicts in Syria and Yemen.

The Iranian effort had a number of goals, according to the Atlantic Council’s DFR Lab, which studies disinformation. The Facebook pages “promoted or amplified views in line with Iranian government’s international stances,” wrote the DFR lab in its initial analysis. Researchers noticed that the content shared included a strong pro-Iranian government bias, as well as an effort to advance Iranian interests.

In several examples viewed by the DFR lab, the campaign shared content as varied as pro-Palestinian images and conspiracy theory videos that argued the Sept. 11 attacks were an “inside job” executed by the government of the United States.