Approximately 250 soldiers are deployed to the 1,254-mile state-state border with Army National Guard Brig by Monday. Gene. Tracy Norris said
"This mobilization supports the priorities of the governor and the president in securing our borders," she told reporters.
More troops will be sent as mission requirements and locations are set, she added.
Notifications for troops will go in the post Saturday, explaining the troops they will need to report next week, Norris said.
Texas already has 100 National Guard soldiers on the border of another operation, which began in 2014.
Another southwestern state announced its National Guard plans. Arizona sends 150 soldiers to the border next week, the military ministry said. The troops will provide air support, help with the reconnaissance and construction of the border infrastructure, and provide logistical support.
A Pentagon spokeswoman, Dana White, said Thursday: "These National Guard members will assist the Border Patrol agents to carry out law enforcement duties."
Earlier, Secretary of Defense James Mattis said the department would consider how they did so support the Department of Homeland Security.
"We will find out," he said. "It will be in accordance with the law and the spirit of Congress, no problem."
Late Friday, he and State Security Minister Kirstenen Nielsen published a joint statement.
"National Guard troops will be deployed tonight to support border security missions along the US Southwest border," they said. "In close cooperation with the border governors, the Department of Homeland Security has identified security issues that could be resolved by the National Guard."
"Raising up to 500 National Guard soldiers on SW border patrol mission vehicles, equipment and helicopters on" Tonight, "Lengyel wrote.
Norris said Texas troops moving on Friday were Planner.
US law limits what troops can do Federal laws prohibit the use of the military to enforce laws, which means that troops can not really participate in immigration, and in the past they have supportive roles
Norris said whether an airman or soldier is armed during the mission depends on the nature of the mission, but the guard is still working with Homeland Security
Mattis signed on Friday a briefing for "up to 4,000 National Guard personnel to support DHS Southern Border Security Mission while under command and control of their governors by September 30, 2018, "according to a ministry of defense
The memorandum says troops will only be armed in limited situations that may require self-defense.
President Donald Trump said Thursday he would send 2,000 to 4,000 troops to the Mexican border.
He said in the memorandum that "the security of the United States is jeopardized by a drastic increase in illegal activity on the southern border".
Deployment of National Guard troops to the Mexican border is not unprecedented. Both Trump's predecessors did so, although the movements were criticized as costly and of limited effectiveness.
Norris noted that the troops will need time to report relatives and employers on their missions.
Troops usually go first to an armory their equipment and are informed before they set off.