"The letter says that ahead of the return of Prime Minister Narendra Modi from his foreign tour, bombs will explode at our party headquarters and other public places," Tamilisai Soundararajan, president, Tamil Nadu BJP told reporters here today.
She said her party had lodged a complaint with police on receipt of the letter.
Recently, similar threat was received by the Kalpakkam Atomic plant and Hindu Munnani office here.
A senior police official said the threat letter to IGCAR and the BJP office appeared to be "similar, a copy and paste," exercise. However, they were looking into it.