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Gyeongbok palace is covered with smoke billowing from a construction site engulfed in flames at a national art museum, right, in Seoul, South Korea, Monday, Aug. 13, 2012. Fire officials in the capital said a large blaze at a construction site near a 600-year-old palace has killed at least four workers and injured about 20. KOREA OUT
SEOUL, South Korea—Fire officials in the South Korean capital say a large blaze at a construction site near a 600-year-old palace has killed at least four workers and injured about 20.

They say Gyeongbok palace wasn't damaged by Monday's fire, which filled Seoul's central district with smoke.

Seoul Metropolitan Fire and Disaster official Kim Byung-ro says the workers died after inhaling toxic smoke. One of the injured is in critical condition.

Kim says the blaze may have started when a spark from construction at the site of a national art museum landed in combustible material.

About 170 firefighters extinguished the fire in about an hour.

In 2008, an arsonist destroyed a gate in Seoul regarded as a South Korean national treasure. It's now being rebuilt.