Presidential Security Service staff members patrol around the presidential residence in Hannam-dong in central Seoul, Monday. Yonhap

President Yoon Suk Yeol ordered security personnel to use weapons against investigators attempting to execute a warrant for his detention over an investigation into his declaration of martial law, an opposition lawmaker claimed, Monday.

Rep. Youn Kun-young of the main opposition Democratic Party of Korea (DPK) made the claims based on reports he says he received from staff members of the Presidential Security Service (PSS).

His remarks come amid a weeks-long standoff between the PSS and a joint investigation team seeking to execute the detention warrant. Yoon has remained at his residence in Hannam-dong, central Seoul, which is heavily guarded by hundreds of PSS members.

"There are continuous tip offs that Yoon is urging his guards to use weapons," Rep. Youn said during a press conference at the National Assembly.

According to the lawmaker, Yoon had lunch with six senior PSS officials on Sunday and told them to prevent police officers from approaching his residence by using a knife, if a gun was not allowed.

The lawmaker's claim follows a similar report by a local newspaper, which said Yoon had a separate meal with PSS officials on Saturday and instructed them to consider using force if investigators attempted to execute the warrant.

"Under the current law, it is clearly illegal for PSS guards to use weapons such as guns and knives in this situation. Yoon should reveal to the public whether he gave such illegal orders," the lawmaker said.

He also pointed out, "Many security officers who have risked their lives for the presidents of the Republic of Korea are not private soldiers hired for an individual."

He added that a PSS staff member, in a text message sent to him, expressed deep disappointment at the president's order to illegally use weapons for his protection.

"(Yoon) should not ask them to become criminals if he has any sense of responsibility as the president of Korea," he said. "The more Yoon shows madness with some security forces backing him, the more it proves why he should be detained and why impeachment was justified."

Rep. Youn Kun-young of the main opposition Democratic Party of Korea speaks during a press conference at the National Assembly in Seoul, Monday. Yonhap

In response to the claim, Yoon's lawyer, Yoon Kap-keun, dismissed it as "fake news."

"The president only emphasized the proper performance of duty according to the standard security manual, and he never issued such an order," the lawyer said. "The PSS staff has been trained by the same manual, following the same principles for decades across all administrations, and they have carried out their responsibilities accordingly."

Amid the ongoing confrontation, a joint probe team announced on Monday that it had sent a letter to the PSS requesting its cooperation in detaining the president and warned of legal consequences for refusing to comply.

The letter warned that security personnel obstructing the execution of the warrants could face criminal charges, the potential loss of their status as public servants, and restrictions on rehiring and pension benefits.

Meanwhile, Park Chong-jun, the former head of the PSS who resigned on Friday, underwent police questioning for the third time on Monday over allegations of obstructing official duties, as he led the effort to block a detention attempt by investigators on Jan. 3.

Several other senior PSS officials have refused to appear for police questioning and the probe team plans to seek detention warrants against them.

Later in the day, acting President Choi Sang-mok ordered the police and the PSS to "ensure the orderly enforcement of the law and the safety of working-level officials."

"All law enforcement actions must be conducted in a peaceful and restrained manner. Under no circumstances should violence be employed by any involved agency," Choi said in a press release.

The PSS heightened security at Yoon's residence by installing barbed wire, barricades and buses to block access to the compound.

Prof. Cha Sung-an of University of Seoul Law School, second from left, and others try to deliver a letter to Presidential Security Service (PSS) officials in front of the presidential residence in Seoul, Monday, urging PSS staff to reject orders, allegedly from President Yoon Suk Yeol, to use weapons to stop police from trying to detain him for declaring martial law. Yonhap

Despite repeated calls from the probe team to order the PSS to stand down, Choi has so far refrained from taking sides.

During their meeting at the National Assembly, Rep. Kwon Young-se, chairman of the ruling People Power Party's emergency response committee, urged Choi to instruct all relevant agencies to refrain from what he called the "unreasonable" execution of the warrant to detain Yoon.

In contrast, DPK leader Rep. Lee Jae-myung said, "The most important thing for the acting president is to prevent (Yoon) from forcefully stopping the police from executing warrants issued by judges," pressuring him to actively order the PSS to comply with the warrant.