South Korean authorities ordered brief neighborhood evacuations on Tuesday after a leak of white phosphorus inside the U.S. Osan Air Base south of Seoul, the Safety Ministry said.

No casualties were reported and the evacuation notice for residents was lifted after about half an hour, as South Korean fire authorities and U.S. forces carried out decontamination work, Yonhap news agency reported.

“At 1708 (0808 GMT), due to a ground mishap and out of an abundance of caution, Osan AB (Air Base) established a 1,000-foot safety cordon to protect base and local populace,” the base said in a statement.

“Our emergency response professionals are currently managing an isolated situation on the installation. We are handling this matter with the utmost care and expediency.”

A spokesperson for the air base said there was a munitions-related accident and it was assessing the situation, in response to a request to confirm the nature of the leak.

White phosphorus is a highly toxic substance that can ignite on contact with air and is used in battlefield smoke screens and incendiary weapons.