Houston, TX – Two people were rushed to the hospital on Tuesday morning after being exposed to an unknown substance sent in the mail to U.S. Senator Ted Cruz’s Houston campaign office.

The Houston Fire Department dispatched a HAZMAT team to assist responding firefighters and police, KTRK reported.

Campaign staff reported the piece of mail containing a white powdery substance to authorities right after it was opened on Oct. 2, according to The Hill.

The Houston Fire Department tweeted that it had transported the two people who were exposed to the unknown substance to the hospital.

The fire department said it had evacuated the 9th floor of the Phoenix Tower, located at 3200 SW Freeway, while HAZMAT determined the nature of the substance found in the envelope.

Later, Houston fire officials tweeted that the substance had not tested positive for hazardous materials, and that the evacuation order on the Phoenix Tower had been lifted.

Meanwhile, the Federal Bureau of Investigations was investigating two packages suspected of containing ricin that were delivered to the Pentagon on Monday, NBC News reported.

A source familiar with the investigation told NBC News that the packages were addressed to U.S. Secretary of Defense James Mattis and Chief Naval of Naval Operations Admiral John Richardson.

Pentagon Spokesman Colonel Rob Manning released a statement on Monday that said the Pentagon Force Protection Agency “detected a suspicious substance during mail screening at the Pentagon’s remote screening facility.”

Both envelopes were intercepted at the screening facility located on the Pentagon campus, and neither made it to their intended targets, according to NBC News.

There were no indications that anyone was actually exposed to whatever substance was contained in the envelopes.

Initial field tests indicated the presence of poison believed to be ricin, but the FBI has not said whether those analyses had been confirmed, NBC reported.

The FBI is the lead agency investigating the incident.