A Long Island gay advocacy group has been receiving hateful letters in the mail, including one Thursday threatening to burn down a planned housing center for gay seniors, an official said.

David Kilmnick, CEO of Long Island GLBT Network, said the center received identical letters at its Woodbury center in Nassau and its Bay Shore center in Suffolk on Thursday.

The expletive-filled letter stated in part: "Thought you got the message we are targeting you."

It went on to say the planned senior housing on Bay Shore "won't be safe."

"You are not safe, you are being tracked ... It is just a matter of time until the right moments arrive to eliminate you and your locations, and the 'safehouse' is burned to the ground."

Officials announced Tuesday that a 50-unit development is planned for senior lesbian, gay, bisexual and transgender residents at a Bay Shore site.

Kilmnick said it's the second letter the group has received in the past four months and the third in the last 18 months, and that each has gotten progressively more violent and threatening.

A past letter threatened to turn the Long Island Pride Parade into a scene much like the Boston Marathon bombing, according to Kilmnick.

"These letters are a reminder that we still live in a world that is not safe and where hate and violence against the GLBT community is still an issue that we need to be vigilant about and attack head on," said Kilmnick.

"We have made sure to alert all our staff to be cognizant of our surroundings, parking lots and hallways to ensure the safety of everyone," he said.

The letters were turned over to the Suffolk and Nassau police departments, Kilmnick said. Police confirmed they were investigating.

-- Checkey Beckford contributed to this report. Follow Checkey Beckford on Twitter @Checkey4NY