WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Wednesday that he had been granted authority to allow troops on the Mexican border greater powers to help protect border officials, and would await direction from the Department of Homeland Security.

United States Marines fortify concertina wire along the San Ysidro Port of Entry border crossing as seen from Tijuana, Mexico November 20, 2018. REUTERS/Adrees Latif

Reuters reported on Monday that the White House was likely to give troops authority to protect Customs and Border Protection agents stationed along the U.S. border with Mexico if they come under threat from migrants seeking to cross into the United States.

Speaking with reporters on Wednesday, Mattis confirmed that he had been given the additional authority, but would await a request from the Department of Homeland Security (DHS) before deciding how to use it.

“I have the authority to do more, now we’ll see what she asks me for,” Mattis said, referring to DHS Secretary Kirstjen Nielsen. He said he had no immediate intention of changing the mission.

Mattis said, depending on the DHS request, that troops may be given powers to temporarily detain migrants, but not the authority to arrest them. They would only be permitted to detain migrants for “minutes, not even hours” while they hand them over to border agents.

He said troops could help protect the border agents with shields and batons, but would be unarmed.

Two U.S. officials, speaking on the condition of anonymity, said a memo signed by White House Chief of Staff John Kelly gave Mattis the authority to protect immigration agents and if necessary, could include actions like use of lethal force, crowd control, temporary detention and cursory searches.

The deployment of about 5,800 active duty troops to the Mexico border to bolster defenses ahead of the expected arrival of a caravan of mostly Honduran migrants has raised questions in Congress and among legal experts about troop deployments on U.S. soil.

The Pentagon has said in the past that there were no plans for U.S. forces to interact with migrants and that they have been carrying out support tasks.

The Posse Comitatus Act, a federal law on the books since the 1870s, restricts using the U.S. Army and other main branches of the military for civilian law enforcement on U.S. soil, unless specifically authorized by Congress.

“There is no violation of Posse Comitatus, there’s no violation here at all,” Mattis said.

Asked if the border mission could be extended, Mattis said it was dependent on the situation, but at least some troops would be back home before Christmas. He also said that fresh troops could be assigned new missions.

The mission is currently authorized through Dec. 15.