Prominent immigration activist and Pulitzer Prize-winning journalist Jose Antonio Vargas, who has lived and worked in the U.S. without legal documentation for years, was detained by U.S. Border Patrol agents on Tuesday at a South Texas airport.

Border Patrol spokesman Omar Zamora said Vargas was in custody after being stopped going through security at the airport in McAllen, a city only a few miles from the Mexico border. Zamora said he had no other details about the case.

Vargas had been visiting the border city for several days as part of a vigil to highlight the plight of unaccompanied immigrant children coming into the U.S. illegally who have overwhelmed Border Patrol facilities.

But at McAllen/Miller International Airport, Border Patrol agents stand alongside Transportation Security Administration personnel to check documentation — even for domestic flights. On Tuesday morning, Vargas tweeted: "About to go thru security at McAllen Airport. I don't know what's going to happen."

The security checks at the airport — and elsewhere in the Rio Grande Valley — are familiar to people living along the Texas-Mexico border.

Along highways out of the area, drivers are stopped at Border Patrol checkpoints about an hour's drive north of the border. And it's not uncommon for children who entered the country illegally with their parents to grow up in the Rio Grande Valley to stay home when classmates go on field trips along those roadways to San Antonio.

Vargas, a native of the Philippines, was unaware he would have to pass through an immigration check prior to arriving in the city, said Ryan Eller, campaign director for Define American, the advocacy group founded by Vargas.

Read more at the Associated Press