The new leader of the US Department of Defense has scrapped National Native American Heritage Month in the military.

In guidance issued on January 31, Donald Trump's newly appointed Secretary of Defense Pete Hegseth claimed celebrations of Native American Heritage Month run counter to the "warfighting mission" of the department.

Native Americans enlist at a rate higher than any other ethnic group in the United States, including all non-Native and immigrant populations, and played a particularly important role for US forces in the Second World War.

However, Mr Hegseth concluded, with no evidence, that Native American Heritage Month - which has been observed in the US military for 35 years - would "erode camaraderie and threaten mission execution".

Mr Hegseth has cancelled all official celebrations that reference race, gender and culture.

The department, as well as the individual branches of the military, have long celebrated Native American Heritage Month.

The first events took place after then-president George H.W. Bush, a Republican, signed into law a joint Congressional resolution designating November as National American Indian Heritage Month in 1990.

Public Law 101-343, highlights the support that Native peoples provided to the United States in its earliest days, after the declaration of independence from the British Empire in 1776.

The Oneida Nation, for example, served as a key ally during the war of independence.

The law states: "The people and Government of the United States should be reminded of the assistance given to this country's Founding Fathers by the ancestors of today's American Indians, including the support the original inhabitants provided to George Washington and his troops during the winter of 1777-1778, which they spent in Valley Forge."

The celebration has since become known as Native American Heritage Month and, until now, is observed government-wide every November.

Alaska Natives enlist in the military at the highest rates per capita of any racial or ethnic group in the nation.

The contribution of Native Americans have long been recognised as valuable, most notably with service members known as Code Talkers using their Native languages to develop and transmit unbreakable codes during World War II and other conflicts.

The Republican-led U.S. Senate confirmed Mr Hegseth to serve as Secretary by a vote of 51 to 50 on January 25. He received the least support of any Defense nominee in history.

There are 100 US Senators in total. Due to opposition from three Republicans, the vote of Vice President JD Vance was required to break the tie in the chamber, hence the unusual 51-50 vote.

The guidance he issued also cancels events related to Women's History Month, set to begin on March 1.