SEOUL, South Korea — South Korean authorities on Tuesday briefly ordered civilians to evacuate after what they described as a white phosphorus leak at a US military base near the capital, Seoul.

Officials in the city of Pyeongtaek urged nearby residents to move to a safe location and avoid skin exposure after the leak at the Osan Air Base was detected at around 5 p.m. They lifted the evacuation order several hours later, saying decontamination work had been completed, according to text messages sent out by the city.

Police reportedly used vehicles to establish a perimeter of about 1,000 to 1,700 feet (300 to 500 meters) from the base, blocking pedestrians and rerouting vehicles. There were no immediate reports of major disruptions or accidents.

In a statement, the US 51st Fighter Wing did not mention a leakage of white phosphorus but said it established a 1,000-foot (300-meter) safety cordon around the base “due to a ground mishap and out of an abundance of caution” to protect the base and the local populace. It said reports of a general evacuation of the air base were false.

“We are handling this matter with the utmost care and expediency,” it said. “The safety and well-being of our service members, their families, and our Pyeongtaek neighbors remain our absolute highest priority.”

US Forces Korea did not provide further comment about the incident.

White phosphorus is a controversial chemical substance used in incendiary munitions and smoke shells. When ignited, it can burn at extremely high temperatures and can set buildings ablaze and burn human flesh to the bone.