(Adds Trump comments about India)
ABOARD AIR FORCE ONE, Sept 7 (Reuters) - U.S. President Donald Trump said on Friday the United States and Japan have begun discussion 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.
Later in a speech in Sioux Falls, South Dakota, Trump said: "India called us the other day. They said we'd like to start doing a trade deal. First time."
"They wouldn't talk about it with the previous administrations. They were very happy with the way it was," he said without giving further details.
Trump, who is already challenging China, Mexico, Canada and the European Union on trade issues, has expressed displeasure about his country's large trade deficit with Japan, but had not asked Tokyo to take specific steps to address the imbalance.
On Thursday, though, CNBC reported he had told a Wall Street Journal columnist he might take on trade issues with Japan, causing the dollar to slip against the yen JPY= . White House said Trump would push for fair trade.
"The president has been clear that he will fight to promote free, fair, and reciprocal trade with countries around the world, including Japan, that impose a range of restrictions on U.S. market access," White House spokeswoman Lindsay Walters said in a statement.
"The United States and Japan have been in close contact on ways to address such barriers, including through the U.S.-Japan Economic Dialogue."