A bomb set off by suspected Maoist rebels killed two Indian soldiers and wounded at least three as voting got underway in eastern India's Bihar state.
Authorities say a jeep carrying the soldiers to a polling station drove over a landmine in the Munger district.
Maoist insurgents have urged voters to stay away from the polls and threatened to disrupt the election.
Thursday's voting is the third stage of Indian parliamentary elections, which are spread out over a month to give more than 800 million registered voters the chance to cast ballots.
Voting took place in India's capital, New Delhi, the neighboring state of Haryana and some parts of Uttar Pradesh, along with several regions in the east and south.
Many villagers returned to their homes for the first time since being displaced by last year's Hindu-Muslim riots in and around the city of Muzaffarnagar. The sectarian violence left more than 60 people dead and thousands homeless. Most of the victims were Muslims.
The Hindu nationalist opposition party, BJP, is looking to push out the Congress Party after a decade in power, promising to revitalize a stagnant economy.
Outgoing Indian Prime Minister Manmohan Singh has said it would be a disaster if the BJP's Narendra Modi becomes the new prime minister.
India's supreme court cleared Modi of charges of inciting Hindu-Muslim riots in Gujarat in 2002 that killed around 1,000 people.
The last day of the elections is May 12.