"We have stepped up vigil and conducted checks at vital facilities including ISRO," Bangalore Additional Police Commissioner (Law and Order) Kamal Pant told PTI here.
Pant said there has been no Intelligence from either state or central agencies on the possible terror attack, which has been mentioned in the letters.
The letters written in Urdu and English speaks of bloodshed to be carried out at ISRO, National Aeronautics Limited, HAL and other private and public facilities, Pant said.