Musician and comedian Robby Roadsteamer was arrested outside an ICE facility during a protest in Portland, Oregon — while dressed as a giraffe — and the feds are explaining what led up to the bust.

Video of Robby’s Wednesday arrest went viral … it shows him singing outside a federal building in the city, alongside a bunch of protesters … when federal agents come out and grab him and take him inside.

Honchos at the Department of Homeland Security tell TMZ … “This deceptively clipped video features this attention-starved influencer who flew all the way from Massachusetts to trespass on federal property.”

The feds say, “Three times law enforcement officers told him to back up and step off federal property. He continued to disobey law enforcement and moved further on to federal property.”

They add … “Officers continued to warn him to back up. Following his repeated refusal to listen to law enforcement, he was placed under arrest.”

The officers in the clip have “POLICE” patches, but the Portland Police Department tells us the people in the video are NOT from Portland PD.

For his part, Robby says he’s going to sue over his arrest.