Security was tightened Saturday in Delhi, in the restive north-east and other areas where Maoist rebels are active ahead of India's Independence Day, DPA reported.
More than 100,000 army, police and paramilitary troops were deployed in the north-eastern states to foil any attack by separatists, IANS news agency reported.
Five separatist guerrilla groups based in the states of Assam, Manipur and Tripura have called for a 17-hour strike on Sunday's anniversary and a boycott of the celebrations.
Rebel groups in the north-east routinely attack government targets ahead of and on the annual August 15 events. There are more than 30 such groups and their demands range from independence to autonomy.
Soldiers defused an explosive armed with a time device that was planted in a bus station in Sivasagar, eastern Assam, late Friday.
"We have deployed security forces at all vital installations like road bridges, oil facilities, railway tracks and bridges," Assam's inspector general of police P Bhattacharya said.
Over 40 trains scheduled to pass through Assam during the night, most of them long-distance, were cancelled from Saturday to Tuesday, railways spokesperson S Hajong said.
Security was also tightened in areas where Maoist rebels operate, including parts of Chhattisgarh, Jharkhand and Orissa states.
"Police patrolling has been intensified. Vehicles are being checked at all the entry points of the vulnerable areas," the IANS news agency quoted a police official as saying in Orissa capital Bhubaneswar.
The rebels blew up a local government office building in Orissa's Malkangiri district Friday.
In Chhattisgarh state's Dantewada district, more than 60 armed rebels torched six trucks loaded with iron ore, police said.
"The overnight act of Maoists was a planned move to terrorize people ahead of Independence Day," Dantewada's senior superintendent of police SRP Kalluri said.
Thousands of police were deployed in and around Delhi, especially near the mediaeval Red Fort, PTI news agency reported.
Prime Minister Manmohan Singh is scheduled to unfurl the Indian flag and address the nation from the fort's ramparts on Sunday.
Over 40 closed-circuit televisions have been installed in and around Red Fort, and National Security Guard commandos are to be deployed on nearby high-rise buildings.
The US State Department issued an advisory to its citizens Thursday warning of "a continuing threat of terrorism" in India. "Attacks have randomly targeted public places frequented by Westerners" in the past, the statement said. Asia.