Addressing generals and admirals summoned from around the world by Pentagon chief Pete Hegseth, Republican Trump warned that the military would be involved in his crackdowns on a number of Democratic-run cities.

"We're going to straighten them out one by one, and this is going to be a major part for some of the people in this room. That's a war too -- it's a war from within," Trump said in front of a huge American flag in in Quantico, Virginia.

Trump added that he had signed an order to set up a military quick reaction force to quell civil disturbances "because it's the enemy from within, and we have to handle it before it gets out of control."

Trump began his speech by talking about the US military in general terms, saying it was "reawakening the warrior spirit."

But much of the extraordinary, hour-long address had a highly political tone, in a break with tradition by previous presidents who have tended to avoid overt domestic politics when addressing troops.

As the audience of officers remained silent, Trump also lashed out at the media, calling them "sleazebags."

- 'Fat generals' -

Former Fox News host-turned Defense Secretary Hegseth summoned the highly unusual gathering of hundreds of officers last week before Trump then announced that he would also speak.

Striding the stage, the Pentagon chief said the military must fix "decades of decay" as he lashed out at so-called "woke" policies in the military.

Hegseth unveiled directives for US service members to get fit, cut their hair and shave their beards.

He said all ranks of the US military would now be required to take a physical fitness test twice a year, adding that it was "completely unacceptable to see fat generals and admirals in the halls of the Pentagon."

Hegseth also insisted on "grooming standards", adding: "If you want a beard you can join special forces. If not, then shave. We don't have a military full of Nordic pagans."

The speeches by Trump and Hegseth come as the US military faces controversy both at home and abroad, with Trump deploying troops in Los Angeles and Washington, and shortly in Portland and Memphis.

He has also ordered lethal strikes on small, alleged drug boats in the Caribbean, despite questions over the legality of the attacks.

Trump, who has overseen a rare purge of senior officers after taking office, has also ordered strikes on Iranian nuclear sites and Tehran-backed Yemeni rebels.

- 'Wrong compass' -

Hegseth, who recently rebranded the Defense Department as the Department of War, added: "Foolish and reckless political leaders set the wrong compass heading and we lost our way. We became the 'Woke Department.' But not anymore."

He also declared an end to "ideological garbage," citing concerns over climate change, bullying, "toxic" leaders and promotions based on race or gender as examples.

He also took aim at the Pentagon's inspector general -- which is investigating his conduct over the use of the Signal chat with Trump administration officials -- saying the office had been "weaponized"

In May, Hegseth ordered major cuts to the number of general and flag officers in the US military, including at least a 20 percent reduction in the number of active-duty four-star generals and admirals.

Since beginning his second term in January, Trump has also purged top officers, including chairman of the Joint Chiefs of Staff general Charles "CQ" Brown, whom he fired without explanation in February.

Other senior officers dismissed this year include the heads of the Navy and Coast Guard, the leaders of the National Security Agency and the Defense Intelligence Agency, the vice chief of staff of the Air Force, a Navy admiral assigned to NATO, and three top military lawyers.

Hegseth defended the firings on Tuesday, saying: "it's nearly impossible to change a culture with the same people who helped create -- or even benefited from -- that culture."