NOGALES, Ariz. — Pope Francis’s ambassador in the United States led a cross-border Mass on Sunday in an effort to bring awareness to the plight of immigrants and refugees.

Archbishop Christophe Pierre, the Apostolic Nuncio to the United States, was the principal celebrant as the 3 p.m. Mass got underway in both Nogales, Arizona and Nogales, Mexico.

At least 250 people showed up on the Arizona side, said Steff Koeneman, spokeswoman for the Diocese of Tucson. It wasn’t immediately clear how many came on the Mexico side. An altar was erected on both sides of the border.

Some sat in camping chairs or held umbrellas while listening to the Mass in 80-degree weather.

The mass is the third one along the Arizona-Mexico border this year and is organized by Dioceses Without Borders, a group composed of church leaders from around Arizona and the Mexican border state of Sonora.

Diocese of Tucson Bishop Gerald Kicanas says the Mass focused on immigration, a major issue for the church. Pope Francis has been outspoken in favor of immigration reform and humane treatment of migrants.

Prayers were said for Border Patrol agents and others who work around the border.

“His decision to join us is a reminder that this is an issue very important to our Holy Father,” Kicanas said of Pierre’s attendance.

Past border Masses have included the delivery of communion through the fence that divides the U.S. and Mexico, but that wasn’t be the case this time because the Border Patrol won’t allow it, church leaders say. The masses in the past have drawn thousands.

Kicanas says the Mass was also organized to highlight the close relationship between the Diocese of Tucson and the recently founded Nogales, Sonora, diocese.

But the primary focus is to bring attention to immigrants and refugees, Kicanas said.

“The economic migrant is not a criminal. The economic migrant is someone seeking a decent way of life for themselves, for their family,” Kicanas said.

The Church has been vocal in its support of migrants.

When Pope Francis visited Mexico early this year, he gave a special blessing to migrant families along the border in Ciudad Juarez. Francis stood on a specially built platform next to the Rio Grande, which separates the two countries, and offered a silent prayer for thousands of immigrants who died while trying to reach the U.S.

In April 2014, Cardinal Sean P. O’Malley of Boston, one of the pope’s cardinal advisers from around the world, celebrated a Mass at Nogales that did include distribution of Communion across the border fence.

“The desert is lined with the unmarked graves of thousands,’’ O’Malley said. Summoning the memory of the estimated 6,000 people who have perished trying to make the crossing during the last 15 years, he called it long past time for comprehensive immigration reform.

“We are here today to say they are not forgotten,” O’Malley told the 2014 gathering.

The Boston prelate said he regards the defense of immigrants as a priority for the Catholic church tantamount to its fight against abortion.

“This is another pro-life issue,” O’Malley told the Globe. He said doesn’t believe any Catholic who takes church teachings seriously can “support the status quo” on immigration policy.

Crux Staff also contributed to this report.