Washington, Feb 28 (IANS): Eleven persons have fallen ill after a suspicious envelope containing an unknown substance was opened at a US military base in Virginia, authorities said.

The Arlington County Fire Department tweeted that the hazmat (hazardous materials) scare occurred at an administrative building at Base Myer-Henderson Hall, previously known as Fort Myer Base, Xinhua news agency reported.

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

Three of those affected were taken to hospital and were said to be in stable condition, the fire department said.

The US Marines said the suspicious envelope was received at Fort Myer and the building where it was opened has since been evacuated as a 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.