Defense Secretary Jim Mattis has authorized the use of troops and other military resources at the US-Mexico border, US officials said on Friday, bolstering President Donald Trump’s battle against migrants trekking toward the United States.

The officials, who spoke on condition of anonymity, said Mattis’ authorization did not include a specific number of troops, something that would be determined at a later point, and was not itself a “deployment order.”

The Pentagon did not comment on potential troop numbers, which US officials have told Reuters could be at least 800 active-duty troops and begin deploying as soon as Tuesday.

The US military said Mattis had authorized the military to provide “mission-enhancing capabilities” to US Customs and Border Protection, including engineering support to help build temporary barriers and housing.

One US official told Reuters that some of the US troops could be called in to assist with traffic and crowd control on the US side of the border, potentially helping to manage demonstrators. It was unclear as of Friday if any of the US forces would be armed.

Officials stressed that US troops would not be engaged in any law enforcement activities, something that is prohibited under US law, and instead would focus on support roles in areas like infrastructure and logistics.

On Friday, Mexico offered temporary identification papers and jobs to migrants who register for asylum in that country, stepping up efforts to halt the advance of thousands of people from Central America heading to the US border.

The caravan, which began in Honduras nearly two weeks ago and picked up other Central Americans along the way, has angered Trump, who has maintained a hard-line on immigration.

A banner hanging over a bridge on the migrants’ path read: “Your hearts are brave, don’t give up.”

Trump and his fellow Republicans have sought to make the migrant caravan and immigration major issues before the Nov. 6 elections, in which Republicans are battling to keep control of Congress.

Trump pledged during the 2016 presidential race to build a wall along the southern US border with Mexico. But the funding for his signature campaign promise has been slow to materialize. In April, frustrated by lack of progress on the wall, Trump ordered the National Guard to help secure the border.