Authorities are investigating two letters threatening violence toward a mosque and a Muslim community center in Silver Spring, Md., as well as a third letter to a mosque in Virginia.

The two facilities in Maryland — the Muslim Community Center on New Hampshire Avenue and the Islamic Education Society on Veirs Mill Road — said that they each received letters around Feb. 27 that were similar in nature and threatened harm to the people of their faith, according to Sgt. Rebecca Innocenti, a spokeswoman for Montgomery County police.

She said the letters are being looked at as “bias” incidents at this point. It would be up to prosecutors to eventually decide whether there is evidence of such a crime.

NBC 4 was among the first to report on the threats.

Another mosque in Virginia, the Dar Al-Hijrah Islamic Center in Falls Church, reported receiving an envelope Tuesday with a foreign postmark and the phrase “Kill all Muslims” written on it, according to Fairfax County police.

The incidents come at a time of anti-Semitic vandalism and threats throughout the country, including at two Jewish schools in the Washington region.