ISLAMABAD, Nov 23: Security around Zardari House, located in F-8/2, was further tightened after an SMS was received in which the sender threatened to blow it up.

Police said here on Sunday that Station House Officer (SHO) of Margalla Police Station Inspector Mohammad Nawaz Bhatti received the SMS on his mobile phone from a local number.

The police have registered a case against the unidentified sender under 25-D Telegraph Act.

The police said efforts were in progress to trace the accused through the SIM and mobile phone with the help of the Inter-Services Intelligence (ISI).

Besides, the mobile service provider has also been approached to collect the data of the person on whose name the SIM was issued.