Maine's Democratic nominee for the U.S. Senate was arrested on Friday for allegedly refusing to leave a child immigration detention center near the U.S.-Mexico border, according to the Portland Press Herald.

The report says that Zak Ringelstein, who is challenging Independent Maine Sen. Angus King, was arrested at a facility in McAllen, Texas, after being told he was not allowed inside.

"Zak is being arrested right now after trying to deliver toys, books, water, and blankets to children imprisoned in @realDonaldTrump's internment camp," a tweet from his account read on Friday morning.

A later tweet added: "Zak is now a political prisoner of the Trump regime. #FreeZak #mepolitics #resist"

Specific charges remain unclear, and the newspaper reports that Ringelstein was arrested after repeatedly asking authorities to be let into the detention facility. The confrontation was broadcast on Ringelstein's campaign's Facebook page.

Several Democratic lawmakers and members of the media toured a detention facility in McAllen earlier this week. Rep. David Cicilline (D-R.I.) tweeted on Sunday that officials told him 1,147 children have been separated from parents at the facility he toured.

Republican Eric Brakey is also challenging King, who caucuses with Democrats and is favored to win reelection in Maine.