A U.S. Army veteran who served two tours of duty in Afghanistan was deported to Mexico after his application for citizenship was denied because of a felony drug conviction, his lawyer and immigration officials said.

Miguel Perez-Montes, 39, was flown on Friday from Gary, Ind., to Brownsville, Texas, where he was escorted across the border to Mexico, Nicole Alberico, an Immigration and Customs Enforcement spokeswoman, said in a statement.

Perez-Montes, who came to the United States legally when he was 8 years old, was convicted in 2010 of delivering cocaine to an undercover officer, a felony drug charge, and sentenced to 15 years in prison. He was placed into removal proceedings in 2012, while behind bars in Illinois, and had been in ICE custody since Sept. 23, 2016, Alberico said.

Perez-Montes' case rose to prominence after Sen. Tammy Duckworth, D-Ill., an Iraq War veteran, appealed to the Department of Homeland Security on Friday to stay his deportation and review his case.

Perez-Montes enlisted in the Army in 2001, before the Sept. 11 terror attacks. As a paratrooper and private first class in Afghanistan in 2002 and 2003, he began suffering from "severe" symptoms of post-traumatic stress disorder, Duckworth said. He was discharged in 2004.

Seven years later, in 2011, the Department of Veterans Affairs diagnosed him with PTSD related to his service, the senator said.

"Without proper V.A. care, he self-medicated with drugs and alcohol to cope with his PTSD, which eventually resulted in his drug conviction," she added.

His lawyer, Christopher Bergin,.said last week that he planned to appeal the denial of citizenship "as far up the court ladder as we must climb."