U.S. President Donald Trump condemned protests in Portland, Oregon, and violence in "Democrat-run" cities on Sunday as his Republican administration moves to intervene in urban centers he says have lost control of anti-racism demonstrations.

Federal law enforcement officers, armed with a new executive order aimed at protecting U.S. monuments, last week started cracking down on crowds gathering in Portland to protest police brutality and systemic racism.

After a chaotic night in Portland that saw a police association building set on fire and officers shooting tear gas at a group of mothers protesting police brutality, Trump and Portland's mayor traded barbs over who was to blame for the escalating unrest.