US President-elect Joe Biden rang round allies in Seoul, Sydney and Tokyo Thursday, vowing to repair frayed partnerships and reaffirming mutual-defence pacts thrown in doubt by the current White House.

A day after Biden's series of "America is back" calls with European leaders, the former vice president spoke to Australia's Scott Morrison, South Korea's Moon Jae-in and the recently installed Japanese leader Yoshihide Suga.

All three men had already congratulated Biden on his recent election victory over Donald Trump, despite the incumbent's refusal to concede.

Biden's call with Suga included a stark warning from the Japanese prime minister that the "security situation is increasingly severe" around the region, according to an account of the call from Japanese officials.

Suga's unusually frank analysis was met with Biden expressing his "deep commitment to the defence of Japan" and to decades-old treaty obligations, according to his transition team.

During the four-year Trump administration, America's regional allies often questioned whether the mercurial president would uphold long-standing promises to defend them in the event of a military conflagration.

In a move likely to cause protest in Beijing, Biden reportedly confirmed this defence commitment extended to the Senkakus, an uninhabited island chain claimed by both Japan and China which has been a potential flashpoint for decades.

In a separate 14-minute call with Moon, Biden was said to have described the US-South Korea alliance as "the linchpin of security and prosperity" in the region, and vowed to work together on "shared challenges" such as North Korea and climate change.

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

South Korea's presidential Blue House said Moon and Biden had agreed to meet "as soon as possible" after the American's inauguration.

In his call with Australia's leader, Biden received an invitation to visit next year for the 70th anniversary of a security treaty between the two countries. 

Biden also reportedly noted the importance of "confronting climate change", which Australia's conservative government has been notably slow to tackle, despite being party to the Paris climate accord. 

Morrison described the call as "very warm" and said Biden did not raise the issue of net-zero carbon targets, focusing instead on "emissions reduction technologies".

Biden served for decades on the US Senate foreign relations committee -- which saw him travel around the world meeting foreign leaders.

He also served as vice president to Barack Obama, who spent much of his presidency promoting America as a "Pacific power". 

Obama's much-vaunted "Pivot to Asia" and painstaking alliance-building at regional ASEAN, APEC and East Asian summits was replaced by Trump's more transactional approach.

Trump 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. 

Biden is expected to jettison Trump's combative style, but at almost two decades older than Obama, he comes from a generation of US policymakers that were laser-focused on trans-Atlantic relations during the depths of the Cold War.

Biden names chief of staff
US President-elect Joe Biden pressed ahead with his transition Wednesday despite Donald Trump's refusal to acknowledge defeat, naming a seasoned Democratic operative as chief of staff in his first public White House personnel choice.

Biden tapped longtime aide Ron Klain, who previously served as his first chief of staff while vice president, acknowledging the two had a long road ahead in fighting the coronavirus pandemic as well as healing a deeply divided nation.

"His deep, varied experience and capacity to work with people all across the political spectrum is precisely what I need in a White House chief of staff as we confront this moment of crisis and bring our country together again," Biden said.

He made the announcement after visiting the Korean War Memorial in Philadelphia earlier in the day for a solemn wreath-laying ceremony to mark Veterans Day in the US.

President Trump attended a separate, simultaneous ceremony at Arlington National Cemetery outside Washington, in what should have been a moment of national unity but instead highlighted the Republican's refusal to acknowledge election defeat.

The president made no public remarks during the somber wreath-laying ceremony, his first official appearance since the November 3 vote.

Since media called the race four days ago Trump has not addressed the nation other than via Twitter and a written statement released to mark Veterans Day, and has not conceded to Biden, as is traditional once a winner is projected in a US vote.

With Covid-19 cases shattering records across the country and states imposing new restrictions in a push to contain the virus before winter arrives, Trump seems to have all but shelved normal presidential duties.

Instead, he has remained shut up inside the presidential mansion, claiming that he is about to win and filing lawsuits alleging voter fraud that so far have been backed up by only the flimsiest evidence.

Early Wednesday he was tweeting fresh evidence-free claims of election wins and ballot tampering, despite the consensus from international observers, world leaders, local election officials and US media that the vote was free and fair.

Some Republicans were adding their voices to growing calls for the president to concede, with experts warning his refusal to do so was undermining the democratic process and holding up the transition to Biden, who takes office in January.

Among them was the Republican secretary of state for Montana, Corey Stapleton, who heralded the "incredible things" Trump accomplished in office. 

"But that time is now over. Tip your hat, bite your lip, and congratulate @JoeBiden," he tweeted.

- 'Within his rights' -
Some of the most powerful figures in the Republican party -- among them Secretary of State Mike Pompeo and Senate leader Mitch McConnell -- have backed Trump in his bid to undermine Biden's victory, however.

"There will be a smooth transition to a second Trump administration," Pompeo said in a sometimes testy news conference Tuesday, while McConnell has said the president was "100 percent within his rights" to challenge the election in court.

None of the lawsuits appears to have the potential to change the result and even a manual recount announced Wednesday in Georgia where Biden has a paper-thin lead is unlikely to alter the fundamental math.

Trump's victory in Alaska, which US media called for him on Wednesday, putting another three electoral votes in his column, was not enough either.

- 'Honor of a lifetime' -
Biden's Klain pick drew wide praise from Democrats.

Senate Democrat Elizabeth Warren called Klain a "super choice" for chief of staff because he "understands the magnitude of the health and economic crisis and he has the experience to lead this next administration through it."

In the same statement released by the Biden transition team, Klain, 59, said it was "the honor of a lifetime" to be named to the post.

Since his projected win was announced on Saturday, Biden has addressed the nation, set up a coronavirus task force, spoken with world leaders including Trump allies, begun vetting potential cabinet members and delivered policy speeches.

On Wednesday he took congratulatory phone calls from Australian Prime Minister Scott Morrison, Japanese Prime Minister Yoshihide Suga and South Korean President Moon Jae-in.

Meanwhile Trump's only known activities outside the White House before Wednesday had been to play golf twice over the weekend.

Normally routine secret presidential intelligence briefings have been off the daily schedule. He has made no mention of the dramatic rebound in the Covid-19 pandemic across the country.

Trump's only significant presidential action has been the abrupt firing of defense secretary Mark Esper on Monday, which he announced on Twitter.

His failure to concede has no legal force in itself, but the General Services Administration, the usually low-key agency that manages the Washington bureaucracy, has refused to sign off on the transition, holding up funding and security briefings.

Biden's inauguration is on January 20.