Militants on Tuesday afternoon hurled a grenade at the heavily guarded office of the state-owned Bharat Sanchar Nigam Limited in Srinagar killing one person and injuring at least 35.
Police said the grenade exploded near the main billing counter where a lot of people were in a queue to submit bills and apply for new connections.
The injured have been taken to the Sardar Maharaja Hari Singh Hospital. The condition of two of them is stated to be serious.
The BSNL office is located in the heart of the city.
The attack came on the first day of the Muslim fasting month of Ramzan and just days after the Pakistan-based Lashkar-e-Tayiba issued a threat to intensify operations in Kashmir.
No BSNL employee was injured in the explosion.
The BSNL building is guarded round-the-clock by Central Reserve Police Force personnel.
No militant outfit has claimed responsibility for the attack so far.