NEW YORK -- Secretary of State John Kerry says "it is very likely" that China and Russia are reading his emails.

Kerry's remark was in response to a question by "CBS Evening News" anchor Scott Pelley during a wide-ranging interview that aired Tuesday evening.

"It is very likely. It is not ... outside the realm of possibility and we know they have attacked a number of American interests over the course of the last few days," said Kerry. "It's very possible ... and I certainly write things with that awareness."

"CBS Evening News" anchor Scott Pelley, left, interviews Secretary of State John Kerry, right. CBS News

Kerry's comments come amid a flurry of hacking incidents believed to be carried out by foreign countries. In June, the Office of Personnel Management suffered a massive breach of personal information. Officials have told CBS News, all signs point to Chinese hackers as the source.

A month after the OPM hack, in July, it was revealed that the Pentagon's Joint Staff email was breached. U.S. officials suspected Russia was behind the intrusion.

Kerry said the threat of digital espionage and hacking are "of enormous concern" to the administration.

"Spying has taken place for centuries and the latest means of spying is to be going after peoples' cyber," said Kerry. "Companies spend billions of dollars to protect themselves, the United States government does the same."