A federal agent was shot and critically wounded early Friday while working undercover in a joint mission with Chicago police officers on the South Side of the city, authorities said.

The agent with the Bureau of Alcohol, Tobacco, Firearms and Explosives was wounded around 3:15 a.m. in the Back of the Yards neighborhood, police said. He was taken by a police car to Stroger Hospital, where ATF officials said he was stable and expected to make a full recovery.

Officials said the agent, in his late 20s, was shot during an investigation of illegal guns but gave no details. No one was in custody, according to officials.

A $61,000 reward is being for information leading to the arrest and conviction of the shooter.

The wounded agent is part of a strike force formed last June to cut the flow of illegal guns into Chicago and crack down on people repeatedly arrested on gun charges, officials said. Twenty ATF agents were assigned to the task force, along with 20 officers from the Police Department and the Illinois State Police, the Chicago Tribune reports.

In Back of the Yards, the ATF agents have teamed with Chicago police to investigate gang-related rifle shootings that have become more common in that area over the last two years. The Tribune has reported that more than 140 people have been shot — 50 of them fatally — from the fall of 2016 to the end of 2017 by gang members wielding rifles as their use spread across the South and Southwest sides.

Friday's shooting happened almost exactly a year after two Chicago police officers were shot in Back of the Yards a few blocks away. On May 2, 2017, the Deering District officers were riding in a covert van when they were wounded by rifle fire. One suspect was arrested and a second remains at large.