The Federal Bureau of Investigation (FBI) is investigating a letter signed by the "Taliban group" threatening to destroy a gurdwara in Yuba City, California.
The Yuba City police department received the written threat through mail.
The letter, allegedly been sent by a "Muslim union", also contains a threat to destroy the Golden Temple in Amritsar, India, according to appeal-democrat.com
The threat comes as the Sikh community prepares for its 27th annual parade through Yuba City on Sunday, an event attended by close to 60,000 Sikhs from around the state and country.
"We're going to be investigating if there are leads to be followed up on. The main thing is that people should feel like they can go about their business and participate without being too terribly worried," a FBI spokesperson said.
Yuba City is known for its sizeable Sikh community, the area has one of the largest Sikh populations outside the Indian state of Punjab.
The city is among the first places that many Sikhs settled in when they arrived in the US more than 100 years ago.
Each year on the first Sunday of November, Sikhs from across the US, Canada, India and Britain return to Yuba City for a reunion with family and friends and attend the Sikh parade, which commemorates the receipt by Sikhs of their Holy Scripture, the Guru Granth Sahib, in 1708.
Last year's parade drew an estimated 55,000 Sikhs.