WASHINGTON - Eleven people fell ill after a suspicious envelope containing an unknown substance was opened Tuesday at a US military base in the state of Virginia, local authorities said.

The Arlington County Fire Department tweeted that the hazmat scare occurred at an administrative building at Base Myer-Henderson Hall, previously known as Fort Myer Base.

The facility is next to Arlington National Cemetery and close to the Pentagon.

Three people were taken to hospital and are in stable condition, the fire department said in another tweet.

The US Marines said in a tweet that the suspicious envelope was received at Fort Myer and the building where it was opened was evacuated in precaution.

Officials of the military base are coordinating with local hazmat teams and the Federal Bureau of Investigation. No additional details are immediately available as the probe is ongoing.