The Army says a low level of mustard agent has been detected in a building storing chemical weapons at the Pueblo Chemical Depot.

The leak was found Monday when a mobile laboratory drew an air sample from inside the building.

The Army says the air inside the building is being filtered to clear out the agent. It says technicians in protective gear will go inside later to look for leaks from the shells stored there.

Officials say there were no injuries.

A similar incident was reported in April.

Mustard agent is highly toxic and can cause severe skin and lung inflammation, cancer and birth defects.

About 2,600 tons is stored at the Pueblo depot, about 100 miles south of Denver. The agent is slated for destruction.