By Jeff Mason

BRIDGEWATER, N.J. (Reuters) - The threat posed by North Korea was a key topic in phone calls between U.S. President Donald Trump and the leaders of China and Japan, along with trade issues, the White House said on Sunday.

Trump spoke with Chinese President Xi Jinping and Japanese Prime Minister Shinzo Abe ahead of expected meetings with the leaders of Asia's two biggest economies at a Group of 20 nations summit in Germany later this week.

"Both leaders reaffirmed their commitment to a denuclearized Korean Peninsula," the White House said of Trump's call with Xi from his resort property in Bridgewater, New Jersey, where he is spending a long weekend.

"President Trump reiterated his determination to seek more balanced trade relations with America’s trading partners," it added.

Trump has become increasingly frustrated with China's inability to rein in North Korea, and the reference to trade was an indication the one-time New York businessman may be ready to return to his tougher-talking ways on business with Beijing after holding back in hopes it would put more pressure on Pyongyang.

Trump and Xi discussed the "peace and stability of the Korean peninsula", China's Foreign Ministry said, without elaborating.

Ministry spokesman Geng Shuang later told a daily briefing that the United States was "very clear" about China's position on North Korea. Geng did not elaborate on what Xi told Trump about North Korea.

"Negative factors" have affected Sino-U.S. relations, and China has already expressed its position to the United States, Xi told Trump, according to a read-out of a telephone call between the leaders carried by the ministry.

ONE CHINA POLICY

The ministry said Trump told Xi the U.S. government would continue to follow a "one China" policy, under which Washington acknowledges the Chinese position that there is only one China and Taiwan is part of it, and that this position had not changed.

China pays great attention to that reiteration and hopes the United States can "appropriately handle" the Taiwan issue, Xi told Trump, according to the ministry.

On Thursday, the United States targeted a Chinese bank and sanctioned Chinese individuals and a firm for dealing with North Korea and approved a $1.42 billion arms deal with Taiwan - decisions that angered Beijing.

And on Sunday a U.S. warship sailed near a disputed island in the South China Sea claimed by China, drawing a rebuke from the Chinese Ministry of Foreign Affairs.

Trump’s separate conversations with the two Asian leaders followed White House talks with South Korea’s new president, Moon Jae-in, last week in which the U.S. leader called on Asian powers to implement sanctions and demand North Korea "choose a better path and do it quickly."

TRILATERAL SUMMIT

Trump and Abe, in their call, reiterated their commitment to increase pressure on North Korea.

"They reaffirmed that the United States-Japan Alliance stands ready to defend and respond to any threat or action taken by North Korea," the White House said in a statement.

Japan's Chief Cabinet Secretary Yoshihide Suga told a news conference the two countries and South Korea will have a trilateral summit at the G20 meeting, but he didn’t want to speculate on what might be said there.

“It’s important for these three nations to show their strong unity and cooperation both within and without," Suga said. "Things such as strengthening pressure on North Korea or urging China to fulfill even more of a role. Things like this have been agreed on before as well.”

Trump, who held talks with Abe earlier this year at the president’s Mar-a-Lago resort in Florida, has forged a united front with the Japanese leader on the need to exert pressure on North Korea to curb its nuclear and missile development.

During and after a Florida summit with Xi in April at Mar-a-Lago, Trump praised his Chinese counterpart for agreeing to work on the North Korea issue and has held back on attacking Chinese trade practices he railed against during the presidential campaign.

But Trump has recently suggested he was running out of patience with China's modest steps to pressure North Korea, which is working to develop a nuclear-tipped missile capable of hitting the United States, and has been considering moving ahead on trade actions.

Trump has been weighing new quotas or tariffs on steel imports for national security reasons and plans to discuss his concerns at the G20. Washington sees excess global production capacity, particularly in China, administration officials say.

(Reporting by Jeff Mason in New Jersey, Matt Spetalnick in Washington, Ben Blanchard in Beijing and Takaya Yamaguchi in Tokyo; Editing by Bill Tarrant)