The Pentagon has given its backing to a US Army guard who reprimanded a group that included US Defence Secretary Pete Hegseth at the Arlington National Cemetery.

A video of the Veterans Day observance event on Wednesday showed Hegseth, his wife, and senior advisers laughing and talking while posing for photos in front of the Tomb of the Unknown Soldier.

The footage showed the army sentinel on duty stepping towards Hegseth's group and shouting: "All visitors will maintain an atmosphere of silence and respect at all times."

Chief Pentagon spokesman Sean Parnell said in a statement: "While commemorating this solemn day, a soldier correctly and respectfully reminded everyone to maintain decorum."

"The Secretary and the entire Department have always honored - and will always honor - the sacrifices our military men and women have made to keep America safe."

The Arlington National Cemetery etiquette requests that visitors speak quietly and do not engage in disrespectful or disorderly conduct.

The tomb, which is one of the country's most sacred war memorials, marks the final resting place of an unknown soldier who was killed in World War I.

A service member from the 3rd Infantry Regiment stands watch over the tomb 24 hours a day and has done so since 1948.

It is not unusual for them to admonish visitors to the site, according to the BBC's US partner CBS News. They reportedly do so a few times a day.

Earlier, President Donald Trump, Vice-President JD Vance and other top officials attended the annual wreath-laying ceremony at the cemetery.

During his speech at the ceremony, Trump offered his gratitude to uniformed service members who have fought for the country. He also touted what he sees as his administration's success in the Iran war.

"Under this administration, and it was about time, somebody fought back. All of us fought back," he said.

"And we won," Trump said of the Iran war. "It's just a question of when we want to end it. We want to make sure we have a total victory, not a 93% victory."

Trump also pointed out Hegseth during the ceremony, saying he's done a "fantastic job" as defence secretary.

Trump has repeatedly defended Hegseth amid Democratic lawmakers' push to impeach him. On Tuesday, an effort to impeach the defence secretary under accusations that he waged war on Iran without congressional authorisation failed on Capitol Hill. (BBC)