A US combat veteran and National Guard officer was deeply disturbed as he witnessed federal police use excessive force to violently clear peaceful protesters near the White House to make way for US President Donald Trump to pose for photos outside a church last month, he will testify Tuesday.

US Park Police began violently clearing protesters from Lafayette Square on June 1 without apparent provocation or adequate warning shortly after Attorney General William Barr spoke with police leaders, according to written testimony by D.C. National Guard Maj. Adam DeMarco. Hes scheduled to present the testimony at a hearing investigating the incident before the House Committee on Natural Resources .

A short time after the protesters were driven off, Trump strode across the square surrounded by a White House entourage to pose in front of the historic St. Johns Episcopal Church while holding a Bible .

The account by DeMarco, who was the senior National Guard officer on the scene, contradicts Barr, who has insisted that anti-racism protesters were violent and deserved gassing and physical assault by law enforcement that evening. They were not peaceful protesters . Thats one of the big lies that the media is ... perpetuating at this point, the attorney general said in a televised interview last month.

DeMarco, a West Point graduage who served in Iraq, writes that the events I witnessed ... were deeply disturbing to me, and to fellow National Guardsmen.

From my observation, those demonstrators our fellow American citizens were engaged in the peaceful expression of their First Amendment rights. Yet they were subjected to an unprovoked escalation and excessive use of force.

DeMarco said he came forward with his deep concerns to fulfill the oath I swore as a military officer to support and defend the Constitution of the United States.