A New York Times report has claimed that when US President Donald Trump calls old friends on one of his iPhones to "gossip or gripe", Chinese and Russian spies were routinely eavesdropping on the calls.
The daily cited American intelligence agencies over the claims which were published on Wednesday.
The spies were often listening and "putting to use invaluable insights into how to best work the President and affect administration policy", according to current and former American officials.
Trump's aides have repeatedly warned him that his cellphone calls are not secure, The New York Times said.
But the aides have said that the President, who has been pressured into using his secure White House landline more often these days and has still refused to give up his iPhones.
White House officials said that they can only hope he refrains from discussing classified information when he is on them.
The American intelligence agencies had learned that China and Russia were eavesdropping on the President's cellphone calls from human sources inside foreign governments and intercepting communications between foreign officials.
The agencies have also determined that China was seeking to use what it was learning from the calls - how Trump thought, what arguments tend to sway him and to whom he was inclined to listen - to keep a trade war with the US from escalating further.
The Chinese have also pieced together a list of the people with whom Trump regularly speaks in hopes of using them to influence the President, the officials said.
Russia was not believed to be running as sophisticated an influence effort as China because of Trump's apparent affinity for President Vladimir Putin, The New York Times quoted a former American official.
The Chinese and the Russians "would look for any little thing - how easily was he talked out of something, what was the argument that was used", said John Sipher, a 28-year veteran of the Central Intelligence Agency who served in Moscow in the 1990s and later ran the agency's Russia programme.
Officials said that the President has two official iPhones that have been altered by the National Security Agency to limit their abilities and a third personal phone.
Trump keeps the personal phone, White House officials said, because unlike his other two phones, he can store his contacts in it.
None of them are completely secure and are vulnerable to hackers who could remotely break into the phones themselves.