U.S. Secretary of State John Kerry said it is "very likely" his emails are read by the Chinese and Russians, both of whom have been accused of recent cyberattacks on U.S. government targets.
"It is very likely. It is not outside the realm of possibility," said Kerry when asked about the matter Tuesday during an interview on CBS Evening News. "We know they have attacked a number of American interests over the course of the last days."
When pressed further on the issue, the top U.S. diplomat said, "It's very possible. I certainly write things with that awareness."
The U.S. has blamed China for a series of high-profile cyberattacks on U.S. government and business entities in recent years. China has strongly denied the allegations.
One of the most recent instances occurred earlier this year, when hackers broke into the Office of Personnel Management and stole the personal data of more than 21 million federal employees.
U.S. officials suspect China-based hackers are responsible, though the Obama administration has not publicly blamed Beijing for the theft.
U.S. defense officials believe Russia-based, state-sponsored hackers may have been behind a July cyberattack on the Pentagon's Joint Chiefs of Staff email network.
The attack affected about 4,000 military and civilian personnel, though no classified information is believed to have been stolen.
Earlier this month, NBC News reported that Chinese hackers have been accessing the private emails of top U.S. security and trade officials since at least 2010.
The report said the intrusions all involved the private emails of the officials and not government email accounts, which are more secure.
The targeted officials have not been publicly identified. But the time period of the alleged hacking overlaps with Hillary Clinton's use of a private email account when she was secretary of state from 2009 to 2013.
U.S. officials raised the issue of cyberattacks "very, very strongly" in recent dialogue sessions with the Chinese government, Kerry said.
He insisted they would continue to do so when President Barack Obama meets Chinese President Xi Jinping in September at the White House.
"We have agreed to begin to have a working group dig into this more directly because it is an enormous concern," he said.