On his first visit to the Pentagon as president, Biden also sought to break from the policies of his predecessor Donald Trump, promising the US defense force to keep domestic politics out of the country's security.

"I will never dishonor you, I will never disrespect you," he said, as Vice President Kamala Harris and Defense Secretary Lloyd Austin stood at his side.

"I will never politicize the work you do."

In brief remarks after meetings with the Pentagon's top generals and civilian leaders, Biden focused on China as the premier strategic threat to the United States.

He announced a special Defense Department task force on China and ordered an immediate review of the military's strategic approach to the challenge from Beijing.

The move was necessary "so that we can chart a strong path forward on China-related matters that will require a whole-of-government effort," he said.

"We need to meet the growing challenges posed by China to keep peace and defend our interests in the Indo-Pacific and globally," he added.

- 'Meet the China challenge' -

The new task force was given four months to come up with assessments and recommendations on US military strategy toward China; technology, force structure and force posture; and alliances and bilateral defense relations with Beijing.

Biden said the results of the Pentagon review needed to be backed by both political parties and Congress, as well as bring together allies and other partners.

"That's how we will meet the China challenge and ensure the American people win the competition in the future," he said.

Biden, whose late son Beau served in Iraq under Austin, also pledged to keep the military strong.

But both he and Austin highlighted the new administration's "diplomacy first" approach, after Trump jettisoned previous policy for a more robust and aggressive "America First" stance with both allies and adversaries.

"So often, our armed forces and the Department of Defense staff are how the rest of the world encounters America," Biden said.

"But our country is safer and stronger when we lead not just with the example of our power, but with the power of our example."

Biden said he would "never hesitate" to deploy US forces to protect vital US interests but that he believes "force should be a tool of last resort, not first."

- 'Full diversity' reflected at top -

During his visit to the Pentagon, Biden took time out to visit an exhibit portraying the often little-known contributions of African-Americans to the US military.

Both Austin and Harris are the first African-Americans to serve in their positions.

The president noted the 22 Black service members who had won the Medal of Honor, and those who pioneered their way to the rank of general.

"It's all part of a long history of barrier-breaking service," he said.

"Right now, more than 40 percent of our active duty forces are people of color."

Biden said that minorities, who are thinly represented in the Pentagon's officer ranks, need more opportunities.

"It's long past time that the full diversity and full strength of our forces is reflected at every level in this department, including our secretary of defense," he said.