Facebook has identified and deleted more accounts engaged in misleading political behavior ahead of the US mid-term elections in November.

The social network said Tuesday that it had removed 652 pages, groups and accounts linked to Russia and, unexpectedly, Iran, for “coordinated inauthentic behavior” that included the sharing of political material.

Facebook has significantly stepped up policing of its platform since last year, when it acknowledged that Russian agents successfully ran political influence operations on Facebook aimed at swaying the 2016 presidential election.

The social network said it had not concluded its review of the material and declined to say how or why the state-backed actors were behaving the way they did. But it said it has informed the US and UK governments as well as informed the US Treasury and State departments because of ongoing sanctions against Iran.

“There’s a lot we don’t know yet,” CEO Mark Zuckerberg said on a hastily called conference call with reporters Tuesday afternoon.

Facebook said the actions to remove the pages, groups and accounts Tuesday morning were the result of four investigations — three involving Iran and one involving Russia.

The first involved a group called “Liberty Front Press” that set up multiple accounts on Facebook and Instagram that were followed by 155,000 other accounts. The group was linked to Iranian state media based on website registrations, IP addresses and administrator accounts, Facebook said.