The deployment would follow similar moves by the Republican president to mobilize troops against the wishes of local Democratic leadership in Los Angeles and Washington DC.

Trump says the deployments are necessary to crack down on crime and protests against his contentious and wideranging mass deportation drive.

The suit filed by Oregon and Portland authorities on Sunday accused Trump of overreach, saying the move "was motivated by his desire to normalize the use of military troops for ordinary domestic law enforcement activity," particularly in jurisdictions run by his political opponents.

Since returning to power in January, Trump has delivered on campaign promises to go after undocumented migrants in a drive that lawyers and NGOs say has led to frequent violations of people's rights.

In recent weeks, the Republican has also vowed to take on violence he alleges is being carried out by an alleged left-wing "domestic terrorist" network -- moves his critics say are designed to silence dissent.

In its suit, Oregon authorities said there was no need for a National Guard deployment to Portland as -- contrary to Trump's claims -- the protests there against Immigration and Customs Enforcement (ICE) have been small-scale and peaceful.

The suit said the protests typically involve less than 30 people and have not required arrests since mid-June.

"But (Trump's) heavyhanded deployment of troops threatens to escalate tensions and stokes new unrest," the suit said.

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.

Earlier, responding to Trump's Saturday announcement, Oregon Governor Tina Kotek said she had been given no details or timeframe regarding the troop deployment.

"There is no insurrection, there is no threat to national security, and there is no need for military troops in our own major city," she told reporters.

Portland Mayor Keith Wilson called the deployment "unwanted, unneeded and un-American."

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.

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.