Cambodian leaders are warning people to be alert after they received an anonymous letter whose author threatened to shoot Cambodians whom he blamed for setting off fireworks in Mifflin Square Park.

“We take this threat very seriously, especially with the ongoing anti-Asian hate and violence,” Nak Chhoeung, board president of the Cambodian Association of Greater Philadelphia, told families.

The association plans to address the incident during a news conference at 3 p.m. Friday at the park. The letter has been reported to Philadelphia police and other investigative agencies, the association said.

The popular park at Sixth and Ritner Streets is used by Philadelphians of all races and nationalities, the site for everything from art workshops to library programs — and sometimes fireworks.

Police said they have the letter and envelope, and are investigating the threat.

Anti-Asian hatred bloomed with the coronavirus pandemic and was stoked by former President Donald Trump — the fatal shooting of six Asian women in metro Atlanta came on the one-year anniversary of his first “China virus” tweet.

In Philadelphia and elsewhere, some residents have taken to wearing special Yellow Whistles in case they need to summon help. People have signed up for self-defense classes.

Hate incidents increased 194% in the first quarter of 2021, compared with the same period a year ago, in 22 big cities and counties, according to the Center for the Study of Hate & Extremism at California State University, San Bernardino. The total number of incidents filed to police in those places increased from 36 to 106, though many go unreported to authorities.

The typed, one-page letter that was sent to the Cambodian Association office in South Philadelphia was dated June 30 but wasn’t opened until July 5 because of the July 4 holiday weekend.

Its author said Cambodian residents who use the park are igniting fireworks at all hours, preventing him from sleeping. He wrote that Marine tours of duty in Iraq and Afghanistan left him with traumatic stress disorder and that he owns several guns.

“I want to take a gun and go down there and kill these individuals. … I am writing you to let you know when I do freak out and try to kill these people that it is your fault for not going to them and encouraging them (it is in their best interest) to stop doing this and remain alive!”

The association declined to release a copy of the letter, which was obtained elsewhere.

“It’s targeting. It’s specific,” said association executive director Sarun Chan. “This is blatant racial intimidation and a threat to our community.”