LOS ANGELES - A mustard gas leak was detected Tuesday afternoon at a US Army chemical storage site in Pueblo, Colorado, but no one was sickened, a local newspaper reported.

The dangerous vapors were found in a munitions storage facility within the Pueblo Chemical Depot during routine monitoring, the Denver Post reported on its website.

"Highly trained depot employees installed an air filtering device on the earth-covered storage igloo today, in addition to the filtering system already in place," the Army said in a press release.

Army officials said this indicated that one or more artillery shells stored in the igloo are leaking. Workers will begin searching for the source of the leak on Wednesday.

The 23,000-acre (9,308-hectare) facility, situated about 125 miles (201 km) south of Denver, the capital city of the southwestern state, is one of five Army chemical stockpile sites in the United States. It houses 2,611tons (2,369 metric tons) of mustard agent in approximately 780,000 munitions, comprising 7 percent of the nation's original chemical material stockpile, according to the Department of Defense.

The stockpiles will be destroyed at a destruction plant under construction on the compound to comply with an international treaty. The destruction is slated to begin in 2014 and be completed by 2017, the Army said.