The two-time Oscar winner said that she was unaware of the disappearances, house torchings and extra-judicial killings reportedly orchestrated by Ramzan Kadyrov in the southern Russian republic.
"I deeply regret attending this event," Swank said in a written message to The Associated Press on Thursday. "If I had a full understanding of what this event was apparently intended to be, I would never have gone."
Swank issued the message after the Human Rights Watch criticized her - along with Belgian actor Jean Claude Van Damme and British violinist Vanessa Mae - for attending a show that, it says, "trivializes the suffering of countless victims of human rights abuses."
Representatives for Van Damme and Mae have not responded to AP's requests for comment.
On Kadyrov's 35th birthday on Oct. 5, his government organized a lavish concert in Chechnya's provincial capital, Grozny, that has been restored after being flattened during two wars between Chechen separatists and Moscow since 1994.
The celebrities - as well as dozens of Russian politicians and pop stars - showed up to congratulate and lavish Kadyrov with praise from a stage arranged between a gigantic mosque and a newly built business center.
During the birthday show, Swank said that she had been taken by the Chechen government's "passion to make peace and to make something beautiful." She claimed in her apology that her invitation to the concert made no mention of Kadyrov's birthday.
At the show, Swank also appeared to be one of the few women to wear no headscarf even though women in Chechnya are compelled to adhere to an Islami dress code. Those who refuse to obey have reportedly faced threats and harrassment from Kadyrov's feared security forces.
Swank won Oscars for her roles in "Boys Don't Cry" and "Million Dollar Baby." Her screen credits also include "Freedom Writers," "P.S. I Love You" and "Amelia."
Kadyrov is a former separatist rebel who has boasted of killing his first Russian soldier at age 15. He went over to the federal side at the start of the second Chechen war in 1999.
A string of Kadyrov's critics and political rivals have been brutally murdered in recent years in Russia, Austria, Dubai and Turkey. Kadyrov has consistently denied involvement in any of the killings, saying the accusations are fabricated to blacken his name.
The birthday show was the latest in a series of expensive and extravagant events sponsored by Kadyrov's government despite Chechnya's high poverty and unemployment rates.
He has spent millions of dollars to acquire well-bred horses that have competed in some of the world's richest races and to renovate a soccer stadium in Grozny. International soccer legends have visited Chechnya to play friendly matches.
Under Kadyrov's leadership, Chechnya has become relatively quiet, and the insurgent violence has largely migrated to neighboring republics of the volatile North Caucasus region.