WASHINGTON — A flash fire injured four people during construction work at the State Department Saturday, leaving at least one in "life-threatening condition," the State Department and US media said.

The fire broke out around 11 am local time (1600 GMT) "in the course of routine maintenance in the mechanical area of the main state department building," State Department spokeswoman Victoria Nuland said in a statement.

"The DC Fire Department was called to contain the fire. Several maintenance workers were taken to the hospital for treatment," she added.

CNN television, citing firefighters, reported on its website that one person had received life-threatening injuries, two more were "seriously injured," while the fourth hurt his knee after falling from a ladder.

"The fire was quickly extinguished and the main building has been reopened for normal weekend operations," Nuland said, adding that during the fire, "round-the-clock" operations continued with employees evacuated to a standby facility.

Few agency employees were in the building during the US Thanksgiving holiday weekend.

The cause of the incident was under investigation, officials said.