The Pentagon was placed on lockdown on Thursday after a hazardous materials incident prompted fire officials to investigate an air quality issue at the headquarters of the US Department of Defense, defence and fire officials said.

“The Pentagon has sophisticated systems to ensure the safety of the building and its occupants. Those systems have detected an air quality issue necessitating precautionary measures until we determine its significance,” Pentagon spokesman Sean Parnell said in an email. “The Department is executing standard protection protocols, including a shelter-in-place order for the affected area. Response teams are in place and ready to support building occupants.”

CNN reported, citing two sources, that floors two through five in corridors four through seven had been locked down and people evacuated from several floors. Another source quoted by the network said emergency responders were seen wearing full gas masks and chemical protection suits as they entered the building. A message from the Pentagon’s security team said additional testing was required to determine the source of the problem.

The five-sided Pentagon, one of the world’s largest office buildings and the target of a 2001 al Qaeda hijacking, was still under lockdown at the time of reporting. The incident comes on the same day the United States said it had paused planned fresh strikes on Iran after a deal framework was reached, though officials gave no indication the air quality alert was connected to wider security concerns.

Source: Ada Derana (citing Reuters).