Police stormed a building occupied by squatters in central Seoul on Tuesday, sparking a clash and a blaze that killed at least four people and left 17 injured, officials said.

Commandos raided the four-story building in the Yongsan neighborhood to break up a strike waged by some 40 people camped inside to protest a redevelopment plan, said a Yongsan fire official, who spoke on condition of anonymity because he was not authorized to speak to the media.

The squatters fought back by hurling Molotov cocktails at police, the cable news network YTN reported. One of the burning bottles sparked a fire on the roof, the report said. Photos and footage showed flames engulfing the building and black smoke billowing into the sky.

Paint thinner used in the makeshift explosives may have sparked the fire, officials said, according to the Yonhap news agency.

At least four people were killed, the fire official said. Twelve officers and five others were taken to hospitals with injures, he said.

Police said the squatters had been occupying the building not far from the U.S. Army's Yongsan military base since Monday, but had no further details about them.

YTN said they had been pressing for temporary housing.

President Lee Myung-bak, who replaced the country's top police chief on Sunday, has ordered an investigation into the incident, Yonhap said.