One of South Korea's top actors apologized after it was revealed he fathered a child with a woman he is not married to, sparking nationwide scrutiny in a country where births outside marriage are still seen as taboo.

Jung Woo-sung, an A-lister in South Korea's competitive film industry since his debut in the 1990s, made headlines this week after his agency confirmed the 51-year-old actor is the biological father of model Moon Ga-bi's son born in March.

Days earlier, Moon, 35, revealed she had recently become a mother, without disclosing the identity of the child's father. A local news report claimed that the model had wanted to marry Jung to "provide her child with a family", but the actor declined.

Although Jung vowed to "fulfill his responsibilities" as a father, his silence on plans to marry Moon sparked intense backlash, with many calling him "irresponsible", in a society where deep-seated stigmas against unmarried mothers and their children persist.

"I am truly sorry to all those who have shown me love and believed in me for the concern and disappointment I have caused," Jung said late Friday as he took the stage as a presenter at the Blue Dragon Film Awards.

"I will accept and bear all the criticism. As a father, I will fulfill my responsibilities to my son until the very end."

Jung has long cultivated a scandal-free image, and had served as a goodwill ambassador for the UN refugee agency for nearly a decade until July. 

Critics this week have compared the baby's situation to that of refugees -- highlighting the stigma faced by children of unmarried mothers. 

"He has talked so much about (welcoming) refugees, yet he has made his own son a refugee," said one commenter on a news website.

One lawmaker from the opposition Democratic Party voiced support for accepting different family structures in South Korean society. 

"The reality is that everyone is unique," said lawmaker Lee So-young, who added that her parents divorced when she was young. 

"A society that respects these differences would surely be a better society, wouldn't it?"

Only 4.7 percent of South Korean babies last year were born outside of marriages, one of the lowest among 38 developed countries where the average is around 40 percent. 

South Korea has been battling the world's lowest birth rates and plummeting marriage rates. 

Experts say a contributing factor could be the country's narrow legal definition of what a family entails. 

They point out that court approvals for the adoption of a child by an unmarried individual are extremely rare, seeking sperm donation is effectively banned for unmarried women, and same-sex marriages are not legally recognized.