The deployment comes as a caravan of Central American migrants travels through Mexico toward the US, becoming a flashpoint of Trump’s ire.

The states of Texas and Arizona on Friday said they were sending nearly 500 National Guard troops southwest as part of a White House plan to secure what it insists is a dangerous, porous border with Mexico.

The troops from Texas and Arizona are well below the “2,000 to 4,000” suggested by President Trump on Thursday, but officials with the National Guard said details of mission were still being worked out with the Department of Homeland Security.

Arizona was the first of the four southwest border states to specify the number of soldiers that would be sent in support of the Trump administration’s operation when the state’s Republican governor, Doug Ducey, said 150 troops would be deployed. On Monday, he upped the number to 225, saying on Twitter that that they will be helping “with any support role responsibilities that they need,” and will be stationed in the Tucson and Yuma sectors.

Brigadier General Tracy Norris of the Texas National Guard said 250 troops would also be sent in the next 72 hours in response. Notifications would be sent out to troops Saturday so they could notify their families and employers about their deployment orders, she said.

“The Texas National Guard is a force that is trained and ready with firsthand knowledge of this mission, this area, and a longstanding relationship with state and local law enforcement,” Norris said.

Norris would not offer details as to what activities the 250 soldiers would undertake, where they would be sent, or if they would be armed. Those details were still being worked out with DHS and US Customs and Border Enforcement, Norris told reporters.

DHS and White House officials have also not provided details on what the duties of the troops will be, especially considering that Pentagon regulations prohibit National Guard troops from searching vehicles, or pursuing and arresting anyone.

“We are working with the Department of Homeland Security on what the requirements will be,” Norris said.

Homeland Security Secretary Kirstjen Nielsen and Secretary of Defense James Mattis issued a joint statement Friday night, thanking the Texas and Arizona governors.

“Working with the border governors, the Department of Homeland Security identified security vulnerabilities that could be addressed by the National Guard,” the statement read. “We appreciate the governor’s support and are dedicated to working with them to secure the national borders.”

The Texas National Guard already has 100 soldiers on the border conducting “observe and report” duties, she added.

New Mexico Gov. Susana Martinez also voiced support for the plan, but has not said how many troops would be offered for the operation.

In California, the National Guard said it was reviewing the White House’s request, but is also hoping to receive more information, including about funding and the duration of the mission.

The California National Guard already has about 55 personnel at the border as part of a counter-drug operation.

The Trump administration’s proposal comes at a time when, according to numbers from US Customs and Border Protection, detentions at the border have been at their lowest since 1971.

In fiscal year 2018, the number of detentions dropped to 237,176, down from 271,087 during the same period in 2017.

At the same time, however, a caravan of Central American migrants traveling up through Mexico toward the US has become a flashpoint of Trump’s ire.

The hundreds of migrants reached the Mexican city of Puebla aboard buses Friday, and planned to participate in legal seminars to determine who among them will travel on to the United States and who will make asylum claims in Mexico.