US Secretary of State John Kerry accused China and Russia of "very likely" reading his emails Tuesday, adding that the US has and will continue to discuss cyber attacks with China.

"The answer is it is very likely. It is not ... outside the realm of possibility, and we know that they have attacked a number of American interests over the course of the last days," Kerry said on the TV show CBS Evening News.

His comments came in response to a question from host Scott Pelley about whether he thought the two countries were reading his emails.

Pressed by Pelley, Kerry elaborated. "It's very possible ... I certainly write things with that awareness," he said.

Kerry added that cyber attacks had been a topic of ongoing discussions with China and would be so again when US President Barack Obama hosts Chinese President Xi Jinping in Washington in September.

"Unfortunately, we're living in a world where a number of countries, the Chinese and Russians included, have consistently been engaged in cyber attacks against American interests, against the American government. And it's an issue that we recently raised very, very strongly in our dialogue with the Chinese," Kerry said on the program.

"It's on the agenda for the discussions between President Obama and President Xi when they meet in September. We have agreed to begin to have a working group dig into this more directly because it is an enormous concern."

China is suspected of being behind the cyber attacks, revealed in June, in which massive amounts of personal data on federal employees were stolen, and such attacks were a prominent topic at the Strategic and Economic Dialogue held between the two countries in Washington in late June.

China has said claims it was behind those attacks are unfounded and that it is opposed to all forms of cyber hacking.