The organizers of Boston's "Straight Pride Parade" said they received suspicious letters in the mail Monday, prompting authorities to investigate the items — which turned out to be envelopes filled with glitter.

The Massachusetts State Police bomb squad, the FBI and local authorities all responded after calls came in from Woburn, Salisbury and Malden, WBZ-TV reported. The letters were apparently sent through the U.S. Postal Service with no return address.

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“We, of course, called the police, I mean why would we open something like that," John Hugo, an organizer of Straight Pride, told the news station. "Even if it’s nothing in it, it’s still terrorism as far as I’m concerned because obviously it’s meant to intimidate us."

Another organizer, Samson Racioppi, said "there was tape around [the envelope] where it's sealed. And so all of these are red flags for me." He added that he shook the letter, and "could hear something rattling around inside."

Organizers of Boston's "Straight Pride Parade" were mailed letters full of glitter and Bible verses. (iStock)

"It wasn’t powder, it was bigger than powder, it felt more granular in nature, bigger than sand. I was immediately alarmed of course," Racioppi said.

But what were believed to be threatening letters turned out to contain Bible verses and colored glitter.

The Super Happy Fun America group confirmed in a statement online that "the packages contained no explosive devices or dangerous substances. We are told they found glitter and vague ominous letters."

A fourth letter was reportedly addressed to a Boston City Hall employee. Officials are working to determine if it's connected to the other three letters.

The FBI said there was no immediate threat to the public.

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The Straight Pride Parade is scheduled for Aug. 31 in Boston.