Seoul (CNN) One of South Korea's most prominent animal shelters has been rocked by a euthanasia scandal, amid accusations it secretly put hundreds of dogs to death despite its "no kill" ethos.

This week, a dozen employees of Coexistence of Animal Rights on Earth (CARE) demanded the resignation of the director, Park So-yeon, after a whistleblower came forward to claim the shelter had secretly euthanized more than 230 dogs in the past three years.

In a statement posted online , Park admitted to euthanizing some animals at the CARE-animal shelter, but said it was a limited number and only done as a last resort for ill dogs. CNN has reached out to Park for further comment.

CARE has long spearheaded campaigns to rescue animals from the South Korean dog meat trade. The shelter gained national attention in 2017 after President Moon Jae-in adopted the country's "first dog," named Tory, from the shelter. Moon, a longtime animal rights proponent, posed for photos with CARE staff, including its director.

South Korean President Moon Jae-in (left) pictured alongside CARE director Park So-yeon (right) during the adoption of "first dog" Tory.

No kill?

Last week, a senior manager at CARE, Lim Hee-jin, told the South Korean investigative website Newstapa that Park had secretly been putting dogs down for years, while promoting the shelter as a "no kill" sanctuary.

Lim did not respond to multiple attempts to reach her. CARE staff said she was unavailable for interview.

"Only a few executives were aware. I asked her to just come clean: Say that we were holding them but had to put them down. We can honestly tell people that," Lim said in an interview with broadcaster CBS. "She said no, because we had euthanized too many."

The generally adopted standard for "no kill" shelters is to save more than 90% of animals , and most do carry out limited euthanasia -- of very sick or aged animals, or due to mass overcrowding.

According to Lim, CARE policy of 100% rescue rate quickly led to overcrowding. As a result, Park allegedly began euthanizing animals, beginning with sick and aggressive dogs, but then more generally.

Lim provided Newstapa with an invoice -- later posted online -- allegedly from an animal carcass collection company, which billed CARE for collection of 5.7 tons of carcasses between 2015 and 2018. A CARE employee told CNN he had seen the document and confirmed the figure, but it is unclear how many of the carcasses were the result of euthanasia or natural deaths.

The case against Park was further bolstered by the leaked recording of a conversation, allegedly between Park and Lim, that appeared to support claims that she willfully euthanized healthy dogs.

In the recording, which CNN has heard but not been able to independently verify, a woman can be heard discussing how to cover up the deaths of half a dozen dogs rescued from the country's dog-fighting circuit.

The rescue of the dogs in 2016 had been heavily publicized by Park. But when the members of the media requested Park provide an update on their whereabouts later that same year, the woman in the call is heard suggesting they buy new dogs to cover up their deaths.

"We need to say they were ill or just expired," the woman's voice says in the leaked call. "If we say that some perished, it won't be an issue. How will we fit the number? If we bring many of them from one place at once, it will be suspicious. If we gather a few here and there, it won't be known. Their snout can be dyed a bit darker."

A CARE staff member cries as colleagues hold up signs calling on the animal charity's director to resign amid accusations she carried out a secret euthanasia program.

Shame and scandal

At a press conference this week, broadcast online , CARE employees held signs saying "Park must resign," and "CARE staff were deceived."

Several of the speakers were overcome with emotion, breaking down in tears as their colleagues spoke of their devastation at the news.

"I'm very ashamed and terribly sorry for the animals that died for no reason," said Lee Mi-hee, who worked at CARE rescuing dogs for two and a half years.

She blamed the situation on a broader pattern of questionable behavior by Park, including "coercive orders, indiscriminate rescues, and leaving unplanned messes for the employees to resolve."

"The fact that this is the result of blindly following her shames me greatly and I'm disappointed in myself," Lee added.

In a statement uploaded to CARE's social media, Park said the group had "tried their best to save them but some animals had to be given up for various reasons in extreme circumstances."

She added that only a small number of animals were euthanized "for unavoidable reasons after a general discussion between staff."

Kim Tae-hwan, CARE's public relations manager, told CNN the staff does "not agree with that explanation."

"The revelations show the number of animals killed was not small at all," he said. "There were many arbitrary orders to euthanize animals."

According to Kim, staff at the shelter were shocked by the report. No one at CARE except for top executives were involved in the euthanasia, he said. Staff are now calling for Park's immediate resignation so the charity can continue operating. They also blamed Lim, the whistleblower, for not coming forward earlier, and helping Park secretly euthanize animals for years.

At the press conference, CARE staff had a new concern: Many donors were cutting funding in response to the news.

"There are still 600 animals in CARE's shelter. Please do not forget about them," animal manager Lee Eun-hye said. "The animals do not deserve this."