Defense Secretary James Mattis approved the deployment of National Guard troops to the U.S.-Mexico border.

The move comes after President Donald Trump requested the Department of Defense (DoD) to help the Department of Homeland Security (DHS) secure the southern border. The President said the illegal activity in the southern border surged and reached a point of crisis. He had no choice but to act.

On Friday night, Sec. Mattis signed a memo stating that the National Guard will deploy up to 4,000 troops to the southern border. The troops will be under the command of their respective governs while supporting the DHS perform its “southern border security mission.”

The troops will not interact with immigrant or perform law enforcement activity. They will only use weapons in “circumstances that might require self-defense. Their mission will last until September 30, according to the memo.

National Guard started sending troops on Friday

In a tweet, National Guard Bureau Chief Gen. Joseph Lengyel said up to 500 troops started moving to the southwest border on Friday night. They are bringing equipment, helicopters, and vehicles with them.

Always Ready, Always There! Moving up to 500 #NationalGuard troops immediately on the SW border security mission. Vehicles, equipment & helicopters on the way tonight. https://t.co/nIjKEY5SSv

— Gen. Joseph Lengyel (@ChiefNGB) April 7, 2018

Arizona Governor Doug Ducey and Texas Governor Gregg Abbot already decided to send National Guard troops starting this weekend. Gov. Ducey tweeted his plan to send around 150 troops.

On the other hand, Gov. Abbot said Texas “has maintained a continuous presence of National Guard members along the border…” His administration “will continue to implement border security efforts…”

Meanwhile, Army National Guard Brig. Gen. Tracy Norris said, "within 72 hours the Texas Military Department will have 250 personnel along with ground surveillance vehicles as well as light- and medium-aviation platforms."

In addition, Brig. Gen. Norris stated that the initial troops will include command and control.

On Thursday, California National Guard spokesman Lt. Col. Tom Keegan issued a statement indicating that they received the request from DHS. They are promptly reviewing it to determine how best they can help their federal partners. In addition, Keegan said they are looking forward to more detail.