The top US military officer says he was wrong to have joined President Donald Trump during his controversial walk to a damaged church near the White House.
The 1 June event created “a perception of the military involved in domestic politics”, Gen Mark Milley said.
Mr Trump walked to the church and held up a Bible after a peaceful protest at the death of African American George Floyd was forcibly dispersed.
The use of troops to tackle the protests has provoked fierce US debate.
Mr Trump has regularly referred to “law and order”, calling in the National Guard to the US capital, vowing to deploy the military to other cities and condemning violent protests.
Some of the mostly peaceful initial protests following the death of George Floyd in Minneapolis last month did turn violent with looting in several cities.
But since four police officers were charged in connection with the death, the protests have been more peaceful, spawning an international movement against police brutality and racial inequality.
Video footage of the death in Minneapolis shows a white officer kneeling on Mr Floyd’s neck for nearly nine minutes.
What did General Mark Milley say?
The chairman of the joint chiefs of staff was speaking in a video for a National Defense University commencement ceremony.
He said: “I should not have been there. My presence in that moment and in that environment created a perception of the military involved in domestic politics.
“As a commissioned uniformed officer, it was a mistake that I have learned from, and I sincerely hope we all can learn from it.”
Gen Milley added: “We must hold dear the principle of an apolitical military that is so deeply rooted in the very essence of our republic.”
He also said he was outraged at the “senseless, brutal killing” of George Floyd.
Gen Milley said: “The protests that have ensued not only speak to his killing but also to centuries of injustice toward African Americans.”
The general was wearing battle uniform as he walked with the president and critics said this suggested his support for the deployment of the military against protesters.
Defence Secretary Mark Esper was also on the walk and, although he has not said he was wrong to be there, suggested in a news conference that he thought the walk was for a different purpose of mingling with troops and inspecting damage.
Senior officials told US media that Mr Trump had yelled at Mr Esper after the conference.