The main opposition party Wednesday called on President Moon Jae-in to take a stand on growing allegations of preferential treatment for Justice Minister Choo Mi-ae's son, as the ruling party dismissed the case as groundless.

The split comes amid renewed allegations that the 27-year-old, surnamed Seo, took an extended leave during his military service in 2017 without getting prior approval. Choo was chairwoman of the ruling Democratic Party at the time.

Other key allegations surrounding the son are his family's reported attempt to get him assigned to a base in Seoul, rather than in Uijeongbu, which is north of the capital, and their reported push to have him selected as an interpreter for the February 2018 PyeongChang Winter Games.

"The president appears to be condoning this matter, but we ask that he make the decision to swiftly resolve it," Kim Chong-in, interim leader of the main opposition People Power Party (PPP), said during a meeting with senior party officials and lawmakers.

A presidential official told reporters Tuesday that Cheong Wa Dae has "no particular comment" to make on the issue and that it has always refrained from commenting on pending investigations by the prosecution.

Prosecutors launched an investigation into the alleged preferential treatment in January, but no progress has been announced.

Rep. Chung Jin-suk of the PPP claimed that even "pro-government news outlets" such as MBC, KBS, Hankyoreh and Kyunghyang can no longer defend Choo.

"These outlets' requests for (relevant) material are flooding the offices of opposition lawmakers," he told the meeting.

The PPP has framed the allegations as another case of injustice similar to the special admissions favors allegedly sought by Choo's predecessor, Cho Kuk, for his daughter.

"A year ago today, President Moon formally appointed former minister Cho Kuk," Hwang Kyu-hwan, a PPP deputy spokesperson, said in a statement. "The president's continued silence hasn't changed then and now."

Cho stepped down a month after taking office amid a massive public uproar over alleged admissions irregularities and dubious investments involving his family.

Choo has denied abusing her power to get special favors for her son. In response to the latest allegations, Choo's ministry sent a text message to reporters Monday saying she has not and has no plans to be briefed on the ongoing investigation. She has also publicly and repeatedly expressed her desire for a swift and thorough investigation, it said.

The Democratic Party continued to dismiss the case as a political offensive by the opposition party.

"We continue to see a situation where there are no facts and only allegations," Rep. Kim Jong-min said during a Supreme Council meeting Wednesday. "The opposition party must cease its political offensive based on falsehood."

Rep. Woo Sang-ho said the allegations were not even worth responding to.

"We should get angry if Seo joined KATUSA through connections only, without taking an exam, but that isn't the case," he said in a phone call with Yonhap News Agency.

Seo served his mandatory military duty in the Korean Augmentation to the United States Army (KATUSA) for the 2nd Infantry Division of the US 8th Army. (Yonhap)