President Moon Jae-in's office offered an apology over alleged irregularities of nominees for top government posts Friday.

The apology came as the main opposition party refused to endorse a joint report on the outcome of a recent confirmation hearing for Prime Minister nominee Lee Nak-yon.

Lee, a former lawmaker and a provincial governor, came under scrutiny over his wife's false registration of residence while working as a public school teacher, a move aimed at being assigned to the school of her choice.

Lee has admitted and apologized for the past wrongdoing.

Still, the decades-old misdeed directly contradicted President Moon Jae-in's election pledge to exclude any person with such history from his consideration for nomination to high government posts.

"The presidential office is working to verify nominees for new ranking government officials with very high moral standards," Moon's chief of staff Im Jong-seok told a press briefing.

"But we do confess the reality of running state affairs is not as easy as making election pledges and ask for your understanding."

The ruling Democratic Party earlier sought to publish the joint report on Lee's confirmation hearing, a prerequisite to a parliamentary vote on Lee's appointment as the new prime minister.

The main opposition Liberty Korea Party refused to sign the joint report and demanded an explanation and apology from the presidential office as the president's nominee for new chief of the Fair Trade Commission Kim Sang-jo has also been found to have falsely registered his residence.

"We cannot but look at possible candidates comprehensively by considering the seriousness and intention (or reasons) of their past wrongdoing, and whether such wrongdoings had been repeated," Im said.

"Still, we offer our apology to the people in that our nominees fell short of their expectations. We also offer our apology to the members of the parliamentary confirmation committee and ask for their understanding," he added.

The ruling and opposition parties have agreed to try and hold their vote on the prime minister-nominee's appointment on Monday at the earliest.

A failure to win parliamentary approval for Lee's appointment may further delay the formation of what will be Moon's first cabinet since his election earlier this month.

All Cabinet members, except the prime minister, do not require parliamentary approval for their appointment.

However, their nomination by the president must be preceded by the prime minister's recommendation under the current law, apparently the reason the new president has only named nominees for two Cabinet members out of 16.

The two were nominated apparently after the Moon administration asked Acting Prime Minister and Finance Minister Yoo Il-ho to recommend the two new Cabinet members, including Yoo's own replacement.

Friday's apology from the presidential office also comes as the government and its ruling party need the main opposition party's consent for nearly all decisions that require a majority of votes in the 299-seat unicameral parliament.

The ruling party controls 120 seats in parliament, while the main opposition Liberty Korea Party and the splinter Bareun Party control 107 seats and 20 seats, respectively.

Regarding the new prime minister nominee's appointment, many believe it will eventually be approved, as the left-leaning opposition People's Party is widely expected to support Moon's decision.

The People's Party controls 40 seats in parliament. (Yonhap)