CISF Additional Director General (Airport security) O P Singh confirmed the development but refused to elaborate.
Sources said the paramilitary has informed the Hyderabad Police about the development after which bomb squads and sniffer dogs have been deployed at the airport.
While the movement of fliers at the airport has not been restricted, frisking and scanning has been intensified and security personnel in mufti have been asked to keep an eye on suspicious movements.
The anonymous threat letter has been handed over to the local police which has tasked its special unit to find out the veracity and source of the letter.
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