Republican U.S. Senate candidate Mark Kirk of Illinois speaks to supporters at an election night rally in Wheeling, Illinois Nov.2, 2010. Reuters/Jeff Haynes

UPDATE: 12:52 p.m. EDT — Republican Illinois Sen. Mark Kirk apologized Friday for comments during a debate that mocked the heritage of his opponent Democratic Rep. Tammy Duckworth. "Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family's service," Kirk posted to Twitter after his comments set off a firestorm of criticism.

During the debate Thursday, Duckworth, who lost both legs in the Iraq War and is of Thai descent, mentioned that her father's side of the family served dating back to the Revolutionary War.

"I'd forgotten that your parents came all the way from Thailand to serve George Washington," Kirk responded.

Kirk's campaign did not apologize in its initial statement after the incident.

Original story:

Republican Illinois Sen. Mark Kirk watched his opponent, Democratic Rep. Tammy Duckworth, a disabled veteran who has been given the Purple Heart, make an impassioned speech during a debate Thursday night about service and entering war with caution. His response was to mock her birthplace and the heritage of her parents.

Duckworth was born in Thailand, her father a Marine, her mother a Thai woman of Chinese descent. Duckworth lost both her legs serving in the Iraq War and said during the debate that if she took Kirk's Senate seat she would promote the United States taking careful consideration before entering war.

"You know my family has served this nation in uniform going back to the revolution, I'm a daughter of the American revolution," Duckworth said. "I've bled for this nation. But I still want to be there in the Senate when the drums of war sound. Because people are quick to sound the drums of war and I want to be there to say, 'This is what it costs, this is what you're asking us to do.' And if that's the case, I'll go. Families like mine are the ones that bleed first, but let's make sure the American people understand what we are engaging in and let's hold our allies accountable because we can't do it all."

Kirk was given 30 seconds to respond. "I'd forgotten that your parents came all the way from Thailand to serve George Washington," he said to Duckworth, then stopped. Silence overtook the room. The moderator, seemingly sensing that was the entirety of Kirk's rebuttal, then moved on to the next question.

"I’m proud of both my father’s side and my mother, who is an immigrant," Duckworth said, via the Huffington Post. Democratic leadership was quick to criticize Kirk and bring up military controversies from his past.

Kirk's comments were "offensive, wrong and racist," said Democratic Senatorial Campaign Committee spokeswoman Lara Sisselman in a statement. "Sen. Kirk has been caught lying about his military record over ten times, but he was quick to launch false attacks questioning Congresswoman Duckworth's family's long history of serving our country."

Kirk served with the U.S. Naval Reserve from 1989 to 2013, but spent much of the 2010 election explaining and apologizing for misstatements about his military career, including claiming to win an award he did not. Politifact this year fact-checked the statement that he misrepresented his service record 10 times and found it to be "mostly true," noting that one claim made by Kirk, and surfaced by Duckworth, remains in dispute.

Kirk has also said racially charged comments before, saying President Barack Obama was acting like the "drug deal in chief" and that people "drive faster" through black communities.

The Kirk campaign released a response to the controversy, but did not apologize. "Sen. 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. Rep. Duckworth lied about her legal troubles, was unable to defend her failures at the VA and then falsely attacked Sen. Kirk over his record on supporting gay rights," said Eleni Demertzis, spokeswoman for the Kirk campaign, in a statement.