Fake accounts posing as company job recruiters or employees were used to dupe targets, according to head of cyber espionage investigations Mike Dvilyanski.

"This effort was highly targeted," Dvilyanski said in a telephone briefing.

"It is hard for us to know how successful this campaign was, but it had all the hallmarks of a well-resourced operation."

Some of the malicious code used in the cyber spying campaign was developed by Mahak Rayan Afraz tech company in Tehran with ties to Islamic Revolutionary Guard Corps, according to Dvilyanski.

Facebook took down 200 accounts it said where used to dupe defense or aerospace industry workers into connecting outside the social network, say by email or at bogus job websites.

The group referred to as "Tortoiseshell" had focused its activities in the Middle East until last year, when it took aim primarily at the United States, according to Dvilyanski.

"This group used various malicious tactics to identify its targets and infect their devices with malware to enable espionage," said Facebook director of threat disruption David Agranovich.

"Our platform was one of the elements of the much broader cross-platform cyber espionage operation, and its activity on Facebook manifested primarily in social engineering and driving people off-platform."

Malware slipped onto devices of victims was designed to glean information including log-in credentials to email or social media, according to Dvilyanski.

Facebook said it appeared fewer than 200 users may have fallen for the ruse, and that those people have been notified of the deception.

Facebook also blocked some of the booby-trapped website links from being shared at the social network, according to executives.

The US tech giant added that it shared findings with internet industry peers and law enforcement.

"We were only part of this campaign, and we are taking action on our platform," Dvilyanski said.