The Trump administration fired most of the board of the US Institute of Peace (USIP) and sent its new leader into the Washington DC headquarters of the independent organization on Monday, in its latest effort targeting agencies tied to foreign assistance work.

The remaining three members of the group’s board – defense secretary Pete Hegseth, secretary of state Marco Rubio and national defense university president Peter Garvin – fired president and CEO, George Moose, on Friday, according to a document obtained by the Associated Press.

An executive order that Donald Trump signed last month targeted the organization, which was created by Congress more than 40 years ago, and others for reductions.

Current USIP employees said staffers from Elon Musk’s so-called “department of government efficiency” entered the building despite protests that the institute is not part of the executive branch. USIP called the police, whose vehicles were outside the building on Monday evening.

USIP is a congressionally funded independent non-profit that works to advance US values in conflict resolution, ending wars and promoting good governance.

Moose, said: “DOGE has broken into our building.” Police cars were outside the Washington building on Monday evening.

The CEO vowed legal action, saying: “What has happened here today is an illegal takeover by elements of the executive branch of a private non-profit.”

He said the institute’s headquarters, located across the street from the state department, is not a federal building. Speaking to reporters after leaving the building, Moose noted: “It was very clear that there was a desire on the part of the administration to dismantle a lot of what we call foreign assistance, and we are part of that family.”

The Doge workers gained access to the building after several unsuccessful attempts Monday and after having been turned away on Friday, a senior US Institute of Peace official said. The official spoke on condition of anonymity due to the sensitivity of the matter.

It was not immediately clear what the Doge staffers were doing or looking for in the non-profit’s building, which is across the street from the state department in the Foggy Bottom neighborhood.

White House spokesperson Anna Kelly pointed to USIP’s “noncompliance” with Trump’s order.

After that, “11 board members were lawfully removed, and remaining board members appointed Kenneth Jackson acting president,” she said. “Rogue bureaucrats will not be allowed to hold agencies hostage. The Trump administration will enforce the President’s executive authority and ensure his agencies remain accountable to the American people.”

Jackson had been seen earlier on Monday trying to get into the non-profit’s building.

Moose said the organization had been speaking with Doge since last month, trying to explain its independent status. Speaking of Trump, he said: “I can’t imagine how our work could align more perfectly with the goals that he has outlined: keeping us out of foreign wars, resolving conflicts before they drag us into those kinds of conflicts.”

Doge has expressed interest in the US Institute of Peace (USIP) for weeks but has been rebuffed by lawyers who argued that the institute’s status protected it from the kind of reorganization that is occurring in other federal agencies.

On Friday, Doge members arrived with two FBI agents, who left after the institute’s lawyer told them of USIP’s “private and independent status”, the organization said in a statement.

Chief of security Colin O’Brien said police on Monday helped Doge members enter the building and that the private security team for the organization had its contract canceled.

The US Institute of Peace says on its website that it is a nonpartisan, independent organization “dedicated to protecting U.S. interests by helping to prevent violent conflicts and broker peace deals abroad”.

The non-profit says it was created by Congress in 1984 as an “independent nonprofit corporation”, and it does not meet US code definitions of “government corporation”, “government-controlled corporation” or “independent establishment”.

Also named in the president’s executive order were the US African Development Foundation, a federal agency that invests in African small businesses; the Inter-American Foundation, a federal agency that invests in Latin America and the Caribbean; and the Presidio Trust, which oversees a national park site next to the Golden Gate Bridge in San Francisco.

The African Development Foundation, which also unsuccessfully tried to keep Doge staff from entering its offices in Washington, went to court, but a federal judge ruled last week that removing most grants and most staff would be legal. The president of the Inter-American Foundation sued on Monday to block her firing in February by the Trump administration.