President Joe Biden reaffirmed Wednesday the United States' commitment to defend Japan in his first phone call with Prime Minister Yoshihide Suga, striking a note of reassurance after the Trump era.

During Donald Trump's administration, America's Asian allies often questioned whether Washington would uphold long-standing promises to defend them in the event of attack.

Trump had publicly mulled withdrawing troops from Japan and South Korea, where more than 20,000 US military personnel are stationed to deter any North Korean military action.

Biden and Suga both urged denuclearization of the whole Korean peninsula in the call -- their first since Biden took office last week.

They discussed Washington's "unwavering commitment to the defense of Japan under Article 5 of our security treaty," the White House said, and Biden reaffirmed "his commitment to provide extended deterrence to Japan."

The US backing "includes the Senkaku Islands" -- an area claimed both by Japan and China, which calls the islands the Diaoyus, the statement said.

The leaders also "discussed regional security issues, including China and North Korea. They together affirmed the necessity of complete denuclearization of the Korean Peninsula."

Suga agreed to visit the United States as soon as possible, telling reporters in Japan after the call that the trip would be planned "while watching the coronavirus infection situation."

'Engage with world again'

The Jiji Press agency said the two leaders did not discuss the Tokyo Olympic Games, which were postponed until this year and could again be threatened by the Covid-19 pandemic.

US Secretary of State Antony Blinken also spoke Wednesday with Japanese Foreign Minister Toshimitsu Motegi and stressed Biden's pledge to "engage with the world again," a State Department spokesman said.

America's clear mention of the Senkakus, an uninhabited island chain which has been a potential flashpoint for decades, is likely to cause anger in Beijing.

While Biden is making a clean break from many of Trump's policies, his team has pledged continuity on some diplomatic issues including taking a hard line on China.

The new US leader sat for decades on the Senate foreign relations committee -- traveling around the world meeting foreign leaders -- before serving as vice president to Barack Obama, who promoted America as a "Pacific power."

Trump during his time in power rattled Asian allies by picking trade fights with China, embracing North Korean dictator Kim Jong Un and openly floating the possibility of withdrawing troops from the region.

Suga spoke to Biden in November after the US election and gave a stark warning that the security situation was "increasingly severe" in the Asia-Pacific region.