South Korea's suspended president Yoon Suk Yeol remains defiant in his newly-fortified residence, with the arrest warrant over his short-lived martial law order set to expire on Monday.

Yoon's security team, which stopped investigators arresting him on Friday, installed barbed wire and barricaded the compound with buses over the weekend, to prevent another attempt.

Yoon had ignored multiple summonses to appear for questioning on insurrection and abuse of power charges, before investigators showed up at his residence - only to call off their operation after a six-hour standoff with the presidential security service.

Investigators may try to extend their warrant. They told the BBC they have asked the police to execute it, in the hope their efforts carry more weight.

The police refused to take over the arrest warrant, saying on Monday that it was legally controversial and its execution should be left to anti-corruption investigators.

Public anger has spiralled in recent weeks, as thousands of protesters braved heavy snow over the weekend, both in support of and against Yoon.

South Korea has been in crisis for the past month, ever since Yoon tried to impose martial law citing a threat from the North and "anti-state forces". The fallout continues as US Secretary of State Antony Blinken visits Seoul, seeking to stabilise ties ahead of a Donald Trump presidency.

Time has almost run out for the investigators leading the criminal case against Yoon.

Yoon's lawyers have claimed that his arrest warrant was "illegal" as the anti-corruption investigators did not have the authority to oversee a case as serious as insurrection.

The presidential security team has cited this as a reason for blocking Yoon's arrest - along with the fact that Yoon remains a sitting president until the constitutional court rules on his impeachment.

"For the PSS, whose primary mission is the absolute safety of the president, to comply with the execution of an arrest warrant amidst ongoing legal disputes would be tantamount to abandoning its duty," security service chief Park Jong-joon said on Sunday.

Mr Park denied accusations that his team was serving as a "private militia" for Yoon.

Yoon's lawyers, who on Monday filed complaints against investigators over the arrest attempt, said Yoon has been "practically detained in his residence".

They also filed an injunction against the warrant, which was rejected by the court, and then said they were considering appealing the decision.

Meanwhile, acting president Choi Sang-mok has resisted the opposition's calls to sack key security officials obstructing the arrest.

The BBC understands that opposition lawmakers had asked investigators to try arresting Yoon again, but "more firmly and with sufficient means".

Investigators could also apply for a new detention warrant, which has to be approved by a judge. That would allow Yoon to be detained for up to 20 days, while an arrest warrant only allows him to be held for 48 hours.

But without a change to either the situation or their approach, it seems unlikely investigators or police will be able to make the arrest.

As seen last Friday, they may again be blocked by the presidential security service which formed a "human wall" to protect Yoon. He himself has vowed to "fight to the end", dividing public opinion and spurring on his supporters, who have been demonstrating for days outside his home.

The tense standoff has also raised urgent questions about the robustness and effectiveness of South Korea's political and legal institutions.

The situation also has consequences beyond domestic politics.

Up until last month, the Biden administration had sung Yoon's praises, delighted by his willingness to work with Washington to tackle the security threats posed by North Korea and China. The US put a lot of effort into helping South Korea repair its strained relations with Japan, so the three countries could address these issues together.

Mr Blinken's ongoing visit to Seoul, where he will meet South Korean foreign minister Cho Tae-yul on Monday, therefore comes at a difficult time for these two allies.

Yoon did not tell the US about his plans to impose martial law, meaning Washington did not have the chance to dissuade him and was unprepared for the chaos that ensued.

Blinken will not want to be drawn on the current political situation. He will instead want to focus on preserving the trilateral cooperation between Seoul, Washington and Tokyo beyond Biden's tenure.

Speaking during a joint presser on Monday, Blinken said the US had "full confidence" in South Korea's institutions, and reaffirmed the US government's "unwavering support for the Korean people as they work tirelessly to uphold those institutions".

"Over the past four decades Korea has written one of the most powerful, inspiring democratic stories in the world," Blinken said.

Korea's democracy has been tested in recent weeks - just as American democracy has faced challenges throughout our history. But you are responding by demonstrating your democratic resilience."

But it's hard to disentangle the domestic and geopolitical situations. South Korea could be months away from electing a new president, and that leader may well want to break with Yoon's foreign policies.

Trump, who enters the White House in a fortnight, will also pursue his own agenda.

Additional reporting by Hosu Lee and Leehyun Choi in Seoul