The Police Commissioner of Mumbai Rakesh Maria received a letter on Sunday that threatened to trigger 1993-type serial blasts in the city, the top cop while briefing media persons on Sunday informed.

The letter challenged the city top cop – ‘if you have the guts than stop this to happen’. The letter mentioned this as‘revenge’ to the massacre of ‘innocent’ Palestinians in Ghaza strip in Palestine in Israeli military action.

In the wake of threat the police has beefed up security at certain important government offices, business hubs, financial centres, suburban trains, railway stations, airports, mono and metro rails and crowded market places that are more vulnerable to such attacks as evidenced in the past.

"We are verifying the authenticity of the letter. However, we are not taking the threat lightly. The crime branch and all police stations have been alerted," said Rakesh Maria. In 2012, the government reviewed Maria's security and provided him a bullet-proof vehicle while he was heading the Anti-Terrorism Squad. Maria enjoys Z-category security now.

The letter has not mentioned the name of any terrorist groups clearly but the police believe Indian Mujahideen behind this threat.

“IM modus operandi enjoys shades of similarity with this as we have experienced in the past,” said a senior cop on condition of anonymity.

The black Friday as the shocking day in 1993 is remembered now – when the tragedy struck Mumbai, had taken scores of precious lives.