McALLEN, Texas >> Prominent immigration activist and Pulitzer Prize-winning journalist Jose Antonio Vargas, who has lived and worked in the U.S. illegally for years, was released by U.S. Border Patrol agents on Tuesday after they detained him at a South Texas airport.

Border Patrol spokesman Omar Zamora said Vargas was stopped going through security at the airport in McAllen, only a few miles from the Mexico border. A spokeswoman for Define American, Vargas’ advocacy group, confirmed his release Tuesday afternoon.

It’s common for the Border Patrol to release people on their own recognizances, with notices to appear in court later. With such notices, people can generally travel throughout the U.S. without being detained again.

Vargas had been visiting the border city of McAllen 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, Vargas knew he could have problems. Border Patrol agents stand alongside Transportation Security Administration personnel to check documentation — even for domestic flights and he was carrying only a passport from the Philippines and a palm-size copy of the U.S. Constitution.

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.

In recent years, some U.S. citizens who object to being asked about their citizenship at the interior checkpoints have taken to refusing to answer agents’ questions or produce identification while recording video that is later uploaded to the Internet.

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.

“We had been to border towns before like San Diego and other places, but we didn’t recognize until here the situation,” Eller said while standing across the street from the Border Patrol station where Vargas was being held. “We tried to prepare for basically every scenario that we could.”

Vargas’ last tweet Tuesday morning was a photograph of his Philippines passport and a palm-size copy of the U.S. Constitution.

Eller confirmed that the only identification Vargas carried was that passport. He said Vargas was en route to Los Angeles and that he had consulted with attorneys before going to the airport. Eller said a “travel partner” was at the airport with Vargas, but that they were immediately separated in security.

Vargas’ attorney didn’t return messages for comment.

Vargas had flown to McAllen last Thursday to take part in the vigil. In an essay he wrote for Politico on Friday, Vargas said he has travelled in the U.S. for years without a problem but didn’t realize that immigration checks are done on those driving or flying out of the Rio Grande Valley in South Texas. Vargas noted he doesn’t have any government-issued U.S. identification.

Vargas went public about his immigration status in a 2011 piece for the New York Times Magazine. He was part of the Washington Post team that won the Pulitzer Prize in 2008 for coverage of the Virginia Tech massacre.

He also directed a documentary called “Documented,” and founded the activist group “Define American.”