"I should not have been there. My presence in that moment and in that environment created a perception of military involvement in domestic politics," General Mark Milley, the chairman of the Joint Chiefs of Staff, said of the controversial June 1 incident.

Milley's comments appeared likely to further strain the already fraught relations between US military leaders and the White House.

They came two days before Trump will appear in person at the graduation ceremony of the elite US Military Academy at West Point.

The ceremony is being held despite the coronavirus pandemic at Trump's own wish, and he often uses such events to lay claim to his bonds with the military and assert his role as commander-in-chief.

But relations have frayed over Trump's move to involve the Pentagon in efforts to quell protests and some looting around the country following the killing of African-American George Floyd by a white Minneapolis police officer.

- Battle uniform -

Milley and Secretary of Defense Mark Esper were both strongly criticized for participating in what was widely seen as a political show by Trump, who walked with officials from the White House to pose in front of St. John's Episcopal Church, holding up a Bible.

Minutes earlier, hundreds of peaceful protestors had been forced from Lafayette Park between the White House and the church by police and National Guard troops firing smoke bombs and tear gas-like pepper rounds.

Milley's presence was particularly criticized as he was wearing his camouflage battle uniform.

Normally military officials wear their formal dress uniform when holding meetings in the White House, and for many it implied Milley's support for Trump's stated desire to deploy active duty US troops against protesters.

In a pre-recorded video message, Milley told new graduates of the National Defense University that pictures of him and Esper walking with Trump "sparked a national debate about the role of the military in civil society."

Trump had summoned Milley and Esper to the White House to discuss the extraordinary measure of using active military troops in addition to National Guards to confront protestors.

Pentagon officials have said both had little time to prepare for the meeting, which caught Milley in his battle uniform and Esper as they were headed to a separate non-public meeting.

Nor did they know ahead of time that National Guard troops were going to clear the park using chemical munitions to force the protestors out, Pentagon officials said.

Several former holders of Milley's position blasted him and Esper for accompanying Trump and allowing the military to be politicized.

"I am deeply worried that as they execute their orders, the members of our military will be co-opted for political purposes," said former Joint Chiefs chairman admiral Mike Mullen.

- Freedom to protest -

Two days later Esper announced that he would not support Trump's desire to invoke the rarely used Insurrection Act to call up active troops to deal with the protests.

That, according to media reports, infuriated Trump, who had to be convinced by White House advisors and senior lawmakers not to fire Esper.

In his speech Thursday, Milley stressed that US citizens have the constitutional right to protest peacefully.

"We should all be proud that the vast majority of protests have been peaceful. Peaceful protests mean that American freedom is working," he said.

"We in the military will continue to protect the rights and freedoms of all American people," he added.

- 'Total confidence -

Trump made no immediate comment on Milley's statement, but it sparked speculation the president could retaliate and fire him.

Senior Republican Senator Lindsey Graham, normally a firm supporter of Trump, said in a tweet that he had "total confidence" in Milley as Joint Chiefs chairman.

"I support his statement in both substance and spirit regarding the recent presidential visit to St. Johns."