Five people were killed Tuesday when South Korean protesters armed with firebombs set an apartment block rooftop ablaze as police commandos tried to evict them, officers said.
They said four residents and one officer died in the blaze started by demonstrators who were staging a sit-in to protest their eviction for a redevelopment scheme.
In a dramatic operation a crane was used to lift the commandos onto the roof of the five-storey building in Seoul's central Yongsan district, where between 30 and 40 people had staged a sit-in since Monday.
Yongsan police chief Baek Dong-San told reporters the residents had stacked three shipping containers on the roof to make a watchtower.
As helmeted commandos approached, he said, protesters atop the tower sprayed paint thinner and threw firebombs at them, starting a blaze that spread across the roof.
The blaze was put out after about 30 minutes and the bodies were found during a subsequent search. Baek said 17 police and six protesters were hurt, with one of the residents in a coma.
Police said they confiscated 150 firebombs, 40 bottles of hydrochloric acid, 1,000 bricks and 700 balls to be used as ammunition for slingshots.
"In consultation with the prosecution, police will thoroughly investigate the case," Baek said. Some 1,400 police were mobilised, media reports said, and 25 people were arrested.
President Lee Myung-Bak ordered a thorough investigation of the incident after being briefed on it at a cabinet meeting.
There have been other fiery protests in South Korea in the past.
A court last October confirmed a 10-year jail sentence on an elderly man who torched South Korea's foremost historical landmark, the Namdaemum Gate, over an unrelated property dispute.
In April 2007 a protester set himself alight outside the venue of free trade talks between the United States and South Korea. He died later.
Another man died last June two weeks after setting himself ablaze in protest at a deal to resume US beef imports. Police mobilised for rallies sometimes carry small fire extinguishers to prevent such acts.