The deployment of National Guard members to the U.S. -Mexico border at President Donald Trump's request was underway Tuesday with a gradual ramp-up of troops under orders to help curb illegal immigration.
California Gov. Jerry Brown, a Democrat, has not yet said how - or if - his state will comply with Trump's request for troops to the border.
Trump has said he wants to send between 2,000 and 4,000 National Guard troops to the southern border to crack down at the "lawlessness that continues" there.
But the captain said about the mission, "if they spot anything that may potentially make it across the river, it is safe to say it's probably an illegal activity".
Trump administration officials have said that rising numbers of people being caught at the southern border, while in line with seasonal trends in recent years, require an immediate response.
Trump's move is not totally unusual: both former Presidents Barack Obama and George W. Bush also deployed the Guard to the border in 2010 and 2006, respectively.
In Mexico City, a caravan of Central American migrants that had been heading north stopped in the Mexican capital.
Members of the Arizona National Guard listen to instructions on April 9, 2018, at the Papago Park Military Reservation in Phoenix. Mexican children who had attended school on the US side of the border showed their passports and paid a toll to cross a bridge over the river and walk home to the Mexican community of Ciudad Miguel Aleman.
Not all the troops will be at observation points or need to carry self-defense weapons, officials say.
"I don't think this is a partisan issue or an identity issue", he said.
Doug Ducey tweeted an updated number saying 225 guard members would be deployed to the border.The original number was 150.
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The global border cuts through Nogales, Sonora, Mexico, rear, and Nogales, Ariz., as seen Monday, April 9, 2018, from Nogales, Ariz.
"What is different now it is happening in a different context and a different narrative", said Fernando Garcia, director of the Border Network for Human Rights, an immigrant advocacy group.
New Mexico will begin with sending 80 troops to the border but 250 are expected to eventually serve, the Santa Fe New Mexican reported.
South Carolina Gov. Henry McMaster, a Republican, offered to send members of his state's Guard as well.
"National Guard personnel will only be armed for their own self-protection to the extent required by the circumstances of the mission they are performing", he said.
Mexico's foreign relations secretary said his government is evaluating its cooperation with the United States.
These range from drug arrests mostly along the Interstate 17 corridor to the occasional traffic stop of a cargo vehicle containing a dozen or more undocumented immigrants, who paid what are called "coyotes" to take them into the U.S.
The country's Senate passed a resolution last week saying Mexico should suspend co-operation with the US on illegal immigration and drug trafficking in retaliation for Trump's move. "All it takes is one mistake", he said.
In the Texas border town of Roma, about a half-dozen uniformed Guard members were seen Tuesday near an global bridge along the Rio Grande.
"It's not good for business, to be frank with you", Villarreal said.