Calcutta, Jan. 23 :    Calcutta, Jan. 23:  A day after the attack on the guards posted in front of American Center on Chowringhee, security was beefed up at vital installations and consulates in the city. Unidentified gunmen shot dead four policemen in front of the Center on Tuesday. Till late on Wednesday, they were untraceable. In the wake of Tuesday's mayhem, steps are also being taken to ensure impenetrable security on Republic Day. The government is taking steps to guard the pavement in front of Writers' Buildings, even as the security phalanx around the building was beefed up, with AK-56-wielding commandos guarding the central gate and the other entrances. Ministers and senior bureaucrats, in cars bearing special stickers, however, have been granted access to the main portico. In an order issued during the day, the state government has asked the police to ensure that the restrictions around the building are maintained. The sleuths are expected to haul up people lurking on the pavement near Writers'. However, the number of policemen and commandos on duty at the Secretariat has not been increased, despite the terrorist strike on Parliament in New Delhi on December 13. But, according to state home department sources, the securitymen have been briefed to be on an optimum state of alert. In addition, the state government is increasing vigil in and around the city in view of the Republic Day parade on Saturday. Policemen with assault rifles will be on guard around the city, including important government offices, consulates and crossings from Thursday. 'We have already raised the security level around the building. Chief minister Buddhadeb Bhattacharjee is being accorded Z-plus category,' said a state government official. Commandos have been provided with AK-56s to guard buildings like Lalbazar and prominent consulates in the city, according to Banibrata Basu, deputy commissioner of police (headquarters). Basu said during the Republic Day parade, nobody will be allowed to carry bags. 'Earlier, we used to have armed policemen only in front of the VIP gallery on Red Road. This time, we will have armed policemen all over the Maidan,' Basu added. Despite the holiday mood in the city on Wednesday, there were armed policemen on duty in the Writers' corridors. The police are also planning to clear the trees near Writers', so that there are no obstructions in case of emergency. A staff list of the PWD's caretaker wing is being drawn up. The maintenance staff will be allowed to stay overnight within Writers' only on production of ID-cards. The garage across the street, along Laldighi, will also be patrolled. Sources said the BBD Bag area will be heavily patrolled, specially the car parking zones.