Thousands of South Koreans have continued to gather for rival protests in Seoul, as investigators prepare another attempt to arrest suspended President Yoon Suk-yeol over his short-lived martial law decree amid warnings against potential bloodshed.

Protesters both for and against Yoon gathered in sub-zero conditions along major roads in the centre of the country’s capital on Saturday, either demanding his arrest or calling for his impeachment to be declared invalid.

Yoon has been resisting arrest in a standoff between his guards and investigators last week, after his failed December 3 power grab plunged South Korea into its worst political crisis in decades.

On Friday, Park Chong-jun, Yoon’s chief of security, resigned from his post after being investigated for blocking the embattled president’s arrest. Park warned that any further efforts to detain the ex-leader must avoid violence.

He told reporters that the current attempt to arrest Yoon was wrong and that “there should not be any physical clash or bloodshed under any circumstances”.

On Saturday, Park was again placed under questioning for blocking Yoon’s arrest.

The country has bristled with tension for weeks after Yoon directed soldiers to storm parliament, where they unsuccessfully tried to prevent politicians from voting down martial law.

Since the failed martial law attempt, the parliament has impeached Yoon, and he has been suspended while awaiting a final decision from the constitutional court about his removal.

In the meantime, prosecutors carried out a separate investigation and had secured a court order for Yoon’s arrest and detention, which the presidential security defied. The arrest warrant expired on Monday.

Kim Seong-hun has taken over from Park as chief of Yoon’s security. He is expected to lead efforts to prevent the execution of a second arrest warrant. According to news reports, Yoon’s guards have reinforced his Seoul compound with barbed-wire installations and bus barricades.

The CIO said it will “prepare thoroughly” for its second attempt to arrest Yoon and warned that anyone obstructing them could be detained.

The National Office of Investigation, a police unit, has also sent a note to high-ranking police officials in Seoul requesting they prepare to mobilise 1,000 investigators for the new attempt, Yonhap news agency reported.

If Yoon is taken into custody, he would become the first sitting South Korean president to be arrested.

Al Jazeera’s Patrick Fok, reporting from Seoul, said there was no indication of when a second arrest warrant for Yoon might be executed, but he said the week ahead could be decisive for the political crisis as Yoon’s first impeachment hearing is set to take place on Tuesday.

“Whether he shows in front of the constitutional court is unclear; he has suggested he may not because of certain legal issues that remain unresolved,” Fok said. “And that is going to complicate this whole process if he does not show up in court.”

Fok said the mood of protests on Saturday remained celebratory and peaceful.

“These could be some of the biggest protests we’ve seen since this political saga unfolded, some reports suggesting there are as many as half a million people on the streets of Seoul,” he said.

“If you came down here, you’d be forgiven for mistaking this for some sort of K-pop concert. These rallies that have been taking place are loud and colourful and are meticulously organised. It’s easy to see why so many people want to be involved.”

Anti-Yoon protester and student Kim Min-ji, 25, told the AFP news agency that the police and the Corruption Investigation Office (CIO) have failed to act decisively.

“Despite our efforts, [Yoon] continues to evade accountability,” Kim said. “It is crucial for us to raise our voices until he is removed from office.”

Yoon supporter Su Yo-hahn, 71, said the sitting president’s martial law declaration which he alleged was to root out antistate forces had “valid reasons”.

“He is someone who was elected by the people and represents our country. Saving Yoon is the way to save our nation,” said Su.

Brandon Kang, a 28-year-old Yoon supporter, told AFP he liked the president because he found him “quite similar to US President-elect Donald Trump, which I really … appreciate”.