Four policemen have been injured in eastern India after separate attacks by suspected Maoist rebels ahead of the country's Republic Day celebrations.
Maoist rebels attacked a police station in Bihar state late on Wednesday night, injuring three policemen.
Rebels also blew up a railway bridge in Bihar, disrupting rail traffic.
Heavy security measures are in place across India for the celebrations which separatist rebels in the north-east and Maoists have both opposed.
More than 50 rebels blew up the railway tracks on a key route linking the capital, Delhi, and eastern India.
"We have placed all the police stations on a high alert and vigil has been beefed up on important government installations"
In the neighbouring state of Jharkhand, a policeman was injured in a clash with the rebels.
Several other explosions have been reported from other parts of the state.
A senior police official told the BBC that the Maoists had been carrying out a campaign calling for a boycott of Republic Day.
"We have placed all the police stations on a high alert and vigil has been beefed up on important government installations," Inspector General of police Rajeev Kumar said.
Colourful parade
Security was tight across India as the country prepared to celebrate its 57th Republic Day national holiday.
Tens of thousands of police and paramilitary troops kept watch at important installations.
Extra security was in place along the route of the main Republic Day parade in the capital, Delhi.
In the past, militants have staged attacks in different parts of the country to disrupt Republic Day.
Security was also stepped up in Jammu and Kashmir, and the north-eastern state of Assam.
The parade, featuring colourful marches by military and police contingents, marks the anniversary of India's foundation as a republic.
Some of India's latest military hardware, including nuclear-capable cruise missiles and tanks, were put on display.
Saudi monarch
King Abdullah of Saudi Arabia was the principal guest at the celebrations in the capital.
On Wednesday the two sides agreed to combat crime and terrorism and promote investment.
For nearly half a century, India and Saudi Arabia were on opposite sides of the Cold War divide.
Delhi saw the kingdom as close to long-time rival Pakistan and also suspected it of supporting radical Islamic groups.
Saudi Arabia never approved of India's relationship with Moscow or its failure to condemn the Soviet invasion of Afghanistan.
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