The Obama administration announced this week it had released nearly 20,000 undocumented immigrants who had been convicted of crimes last year instead of deporting them in a practice House Republicans called "infuriating." The chief of U.S. Immigration and Customs Enforcement defended the agency's decision Thursday to a House committee, arguing that Congress must pass comprehensive immigration reform to fix the nation's many immigration woes, Reuters reported.

"I cannot tell you how disheartening it is to sit here and hear a very important issue related to the topic of immigration reform be bandied about as a political football," top Obama administration immigration official Sarah Saldana told lawmakers sitting on the House oversight committee.

The Obama administration released 19,723 undocumented immigrants last year who had been convicted of crimes even as Republican lawmakers across the nation demanded tougher penalties such as deportation after the high-profile killing of Kathryn Steinle, 32, who was fatally shot in San Francisco by Juan Lopez-Sanchez, an undocumented immigrant and convicted felon who returned to the United States after being deported to Mexico five times. 

Critics of the release policy argue such criminals go on to commit further crimes, including homicides, sexual assaults and drunk driving offenses. House Oversight Committee Chairman Jason Chaffetz said Thursday the practice is "infuriating."

Immigration reform and border security have been central talking points in the 2016 presidential race, with Republican front-runner Donald Trump vowing to build a wall along the U.S.-Mexico border and make Mexicans pay for it. Trump at one point cited Steinle's killing as an example of why the U.S. must strengthen its border security. Democratic front-runner Hillary Clinton has blasted Trump's proposal as inhumane and unrealistic, while promising immigration reform advocates that she would not deport undocumented immigrants who are children. 

The Obama administration has said it deports immigrants who have been convicted of violent crimes. But the White House has also released undocumented immigrants after they served prison sentences and have been deemed not dangerous. Some immigrants can't be deported because their home countries refuse to take them back, Saldana said. 

President Barack Obama has repeatedly urged Congress to pass a comprehensive immigration bill that would allow millions of undocumented immigrants to work and live legally in the United States, but critics argue such a policy overhaul would encourage future illegal immigration. Obama has also sought to work around Congress, passing in 2014 an executive action that has allowed some immigrants to defer deportations and obtain work permits, but Republican lawmakers challenged the legality of the policy. The Supreme Court is expected to rule on the executive action this spring. 

Deportations reached a record high by the end of Obama's first term, with more than 430,000 people removed per year. But after immigrant rights groups pushed back, deportations dropped to 231,000 in 2015, the Washington Post reported.