WASHINGTON - Some 900 National Guard troops are deploying to the U.S.-Mexico border to support Border Patrol operations, but they will not perform any law enforcement functions while on the White House-ordered assignment, Homeland Security officials said Monday.

The majority of the military members who have arrived or are headed to the border are National Guard troops from Texas, with roughly 650. In Arizona, there will be approximately 250, and in New Mexico, about 60.

California on Monday said it would no longer allow its National Guard troops to fulfill the mission as requested by the Department of Defense.

California’s governor had said the troops would participate, but not in immigration enforcement.

President Donald Trump reacted on Twitter early Tuesday:

Looks like Jerry Brown and California are not looking for safety and security along their very porous Border. He cannot come to terms for the National Guard to patrol and protect the Border. The high crime rate will only get higher. Much wanted Wall in San Diego already started! — Donald J. Trump (@realDonaldTrump) April 17, 2018



"Looks like Jerry Brown and California are not looking for safety and security along their very porous Border. He cannot come to terms for the National Guard to patrol and protect the Border. The high crime rate will only get higher. Much wanted Wall in San Diego already started!," he said.

The Associated Press reported the tenuous agreement between the federal government and the state soured over the weekend.

U.S. Customs and Border Protection (CBP) deputy commissioner Ron Vitiello told reporters during a news conference Monday that the troops — which may total up to 4,000 — would be stationed along the border until CBP can bolster its own forces.

In an April 4 memo to the secretary of Homeland Security and the attorney general, President Donald Trump said the troops were needed to curb drugs, gangs and illegal crossings on the U.S. border with Mexico.

U.S. President Donald Trump walks on South Lawn of U.S. President Donald Trump walks on South Lawn of the White House in Washington before his departure to the Customs and Border Protection National Targeting Center, Feb. 2, 2018. U.S. President Donald Trump walks on South Lawn of the White House in Washington before his departure to the Customs and Border Protection National Targeting Center, Feb. 2, 2018.

"The situation at the border has now reached a point of crisis,” he said in the memo.

However, previous presidents also saw the need to deploy the National Guard to assist Border Protection agents in the area. Six thousand were sent under President George W. Bush, while 1,200 were deployed under President Barack Obama, according to the U.S. Department of Defense.

The National Guard will assist Border Patrol at least through the end of September, officials said, by performing tasks such as operating surveillance cameras, maintaining vehicles and clearing brush.

“They will not be law enforcement. They will not perform law enforcement functions,” reiterated Bob Salesses, deputy assistant secretary of defense for Homeland Defense Integration and Defense Support of Civil Authorities (DSCA).

Doug Ducey, the Republican governor of Arizona, one of four southern border states, was eager for troops from his state to join the effort. In an op-ed published April 9, he wrote: “Despite what some may say, our southern border is not secure. The announcement by President Trump to call up the National Guard to support the mission of the Border Patrol is needed and welcomed.”

California's Democratic Gov. Jerry Brown said the state would contribute 400 troops but said that not all would be on the border.

"Let's be crystal clear on the scope of this mission," Brown wrote in the letter to defense secretary James Mattis and Homeland Security secretary Kirstjen Nielsen. "This will not be a mission to build a new wall. It will not be a mission to round up women and children or detain people escaping violence and seeking a better life. And the California National Guard will not be enforcing federal immigration laws."

Rather, the California-based troops would focus on transnational gangs, human trafficking, and arms and drug smuggling "throughout the state," Brown said in the April 11 letter.

That agreement had fallen apart by Monday, however.

CBP’s Vitiello said the planned mission “will continue” without the California National Guard.