A day before the 13th anniversary of the Mumbai serial bomb blasts, a major terrorist strike in the city was averted today with the timely detection of two kgs of explosive ammonium nitrate from the Byculla railway station in central Mumbai.Apart from the explosives filled in a polypack water bottle, police also recovered a pocket-size transformer that could have provided the necessary current if a detonator was to be attached to the explosive device, police commissioner A N Roy said today.The explosives were taken to the Girgaum-Chowpatty in south Mumbai where the anti-terrorist squad (ATS) defused the device. The samples of the explosives were sent for forensic examination.The recovery comes in the backdrop of the twin bomb blasts in the temple town of Varanasi on Tuesday. Police is taking the seizure seriously since it has occurred a day before the 13th anniversary of the Mumbai serial bomb blasts, which claimed 256 lives.Ammonium nitrate was detected after the ATS swooped on a tip off, and found it stored on the loft inside the gent's toilet block at the Byculla railway station. "A high-alert has been sounded in the city and security has been tightened in all places of worship, railway stations and vital installations," Roy said.Mumbai, which has witnessed several terrorist attacks since 1993, has fortunately not seen any major terrorist act in the past two years although the police has foiled two such attempts in the past two months.