A deployment in Portland -- Oregon's largest city -- would follow similar moves by the Republican president to mobilize troops against the wishes of local Democratic leadership in Los Angeles and Washington DC.

It also comes as Trump launches an assault against left-wing activists in the wake of several deadly attacks, which the president and his allies claim are evidence of a "domestic terrorist" network.

"At the request of Secretary of Homeland Security, Kristi Noem, I am directing Secretary of War, Pete Hegseth, to provide all necessary Troops to protect War ravaged Portland, and any of our ICE Facilities under siege from attack by Antifa, and other domestic terrorists," Trump wrote on his Truth Social platform.

ICE, or Immigration and Customs Enforcement, is the main agency carrying out Trump's contentious mass deportation drive.

It was not clear if Trump was authorizing the use of troops at ICE facilities nationwide or just in Portland, where protests have been ongoing for months.

The president added he was "also authorizing Full Force, if necessary," without elaborating.

Protesters in Portland and other cities have intermittently blocked entrances to ICE facilities in recent weeks, prompting some clashes as agents try to clear the area.

Oregon Governor Tina Kotek, a Democrat, said she was seeking more information from the White House.

"There is no national security threat in Portland. Our communities are safe and calm," she wrote on X, urging residents to "stay calm and enjoy a beautiful fall day."

Pentagon spokesman Sean Parnell said the department stood "ready to mobilize US military personnel" to support ICE, without further details.

- 'Terrorist' threat -

Officials in Portland are wary of a repeat of summer 2020, during Trump's first term, when the city saw a surge of violent clashes amid racial justice protests following the police killing of unarmed Black man George Floyd.

Oregon Senator Ron Wyden called Trump's move an "authoritarian takeover of Portland hoping to provoke conflict."

"I urge Oregonians to reject Trump's attempt to incite violence," the Democrat posted on X.

Mayor Keith Wilson said the "necessary" number of troops "is zero, in Portland and any other American city."

Trump first deployed troops in Los Angeles in June, overriding the state's Democratic governor and prompting an ongoing legal dispute over the limits of presidential authority.

That was followed by a surge of troops and federal agents to the US capital, and threats to go into other major cities, including Chicago.

The Portland announcement comes days after a deadly shooting at an ICE facility in Texas, in which one detainee was killed and two severely injured.

Federal officials say the gunman, who died from a self-inflicted gunshot, had sought to target ICE agents from a nearby rooftop.

Weeks earlier, conservative activist Charlie Kirk was shot dead at a university campus.

Following Kirk's assassination, Trump announced that he was labeling the diffuse left-wing "Antifa" movement as a "domestic terrorist group."

The designation has led to worries among Trump's critics that it could be used to broadly suppress dissent in the name of national security.

On Thursday, Trump signed an order directing the FBI to investigate and disrupt "organized political violence," while telling reporters that billionaire George Soros -- a frequent target of right-wing conspiracy theories -- would be an example of someone who should be probed.

Attorney General Pam Bondi has meanwhile ordered federal Justice Department agents to ICE facilities around the country.

"If you so much as touch one of our federal officers, you will go to prison," she said Saturday on X.