U.S. Sen. Mark Kirk (R-IL) is facing criticism for comments he made during a Thursday debate about his Democratic challenger's family military service.

During the U.S. Senate debate, Congresswoman Tammy Duckworth (D-IL,8), an Iraq War veteran who was wounded in combat and lost both legs, spoke about her family's history of military service dating back to the American Revolution. 

In response, Kirk said to Duckworth: "I had forgotten that your parents came all the way from Thailand to serve George Washington."

Duckworth was born in Thailand. Her mother is Thai and her late father was a U.S. Marine veteran whose family served in the military since the American Revolution. 

Kirk's comments were met with silence from the debate crowd. Duckworth did not respond before the moderator asked the next question. 

The Democratic Senatorial Campaign Committee rebuked Kirk's remarks, calling them "offensive, wrong, and racist," and demanded Kirk apologize to Duckworth.

"Senator Kirk has been caught lying about his military record over 10 times, but he was quick to launch false attacks questioning Congresswoman Duckworth's family's long history of serving our country," added DSCC's Lara Sisselman. 

In a follow-up statement, the Kirk campaign called Duckworth a "war hero" but stopped short of issuing an apology. 

"Senator Kirk has consistently called Rep. Duckworth a war hero and honors her family's service to this country. But that's not what this debate was about," reads the statement from the Kirk camp. "Rep. Duckworth lied about her legal troubles, was unable to defend her failures at the VA and then falsely attacked Senator Kirk over his record on supporting gay rights."

UPDATE (3:48 p.m.): Kirk apologized to Duckworth Friday via Twitter: "Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family's service. #ilsen".