U.S. President Donald Trump said Friday the United States and Japan have started discussions over trade, saying that Tokyo "knows it's a big problem" if an agreement cannot be reached, and that India has also asked to start talks on a trade deal.

"We're starting that," Trump told reporters aboard Air Force One. "In fact Japan has called us ... they came last week."

"If we don't make a deal with Japan, Japan knows it's a big problem," he added.