Amidst heightened security, Prime Minister Manmohan Singh today unfurled the tricolour at the ramparts of the Red Fort, which was converted into a virtual fortress due to escalated threat perception as the country celebrated its 60th Independence Day.Singh, accompanied by wife Gursharan Kaur, arrived at the Lahore Gate of the monument in a cavalcade of steel-grey Tata Safaris escorted by a posse of SPG personnel.Dressed in his usual white Kurta-Pyajama and Nehru jacket and sporting his trademark sky blue turban, Singh was received by Defence Minister Pranab Mukherjee, his deputies Rao Inderjit Singh and M M Pallam Raju and Defence Secretary Shekhar Dutt.General Officer Commanding, Delhi Area, P C Bhan then escorted the Premier to the saluting base, from where he took a salute from the three services and Delhi Police Guard. He then inspected the Guard of Honour.Arriving at the rampart where he was greeted by the Defence Minister, his deputy and the three Service Chiefs, the Prime Minister unfurled the tricolour as the national anthem was played to the accompaniment of a 21-gun salute.After unfurling the national flag, Singh made a 45-minute address to the nation. Besides top political and military brass of the country, the gathering at the Red Fort included ambassadors and high commissioners of several countries and school children.