Trump was responding to a question in a Fox television interview in Washington about what bilateral deals he would like to see with various countries including Japan.

Tokyo and Washington are engaged in difficult trade talks as Trump's administration seeks to lower the US trade deficit.

"Almost all countries in this world take tremendous advantage of the United States .." Trump said. "We have a treaty with Japan. If Japan is attacked, we will fight World War Three," Trump said.

"We will go in and we will protect them and we will fight with our lives and with our treasure. We will fight at all costs, right? But if we're attacked, Japan doesn't have to help us at all. They can watch it on a Sony television, the attack."

Japanese Chief Cabinet Secretary Yoshihide Suga, asked about the remarks, said the two governments had not discussed revising the treaty and dismissed the notion that the pact was unfair.

"The obligations of the United States and Japan ... are balanced between both countries," he told a news conference.

Under the decades-old US-Japan security treaty, the United States has committed to defending Japan, which renounced the right to wage war after its defeat in World War Two.

Japan in return provides military bases that Washington uses, including the biggest concentration of US Marines outside the United States on Okinawa, and the forward deployment of an aircraft carrier strike group at the Yokosuka naval base near Tokyo.

If that security pact ended Washington would have to withdraw a major portion of its military forces from Asia at a time when China's military power is growing.

Abe, who has cultivated warm ties with Trump since the US leader took office, has pledged to strengthen Japan's defences.

He also wants to revise the nation's post-war, pacifist constitution to clarify the ambiguous status of its military.

Australian Associated Press