Former Prime Minister Rajiv Gandhi was killed Tuesday in a bomb attack at an election rally in southern India, Press Trust of India reported.

The leader of Congress Party had just emerged from his car in the town of Sriperumbudur, 25 miles southwest of Madras, when the bomb exploded, the agency said.More than a dozen people, including the 45-year-old Gandhi, were killed, PTI said.

Security forces immediately cordoned off the area and were trying to rush casualties to nearby hospitals, the Press Trust said.

Gandhi's mother, Prime Minister Indira Gandhi, was shot and killed by Sikh assassins on Oct. 31, 1984. Her son then took over as prime minister, serving until his Congress Party was defeated in 1989.

Indians cast ballots Monday in a general election, and more voting was scheduled later this week. Gandhi's Congress Party was trying to stage a comeback from its 1989 election defeat.

Public opinion polls predicted Gandhi's party would win the largest number of seats in the election.

At least 185 people were killed in earlier violence linked to the election - most before the vote began - officials and news reports said.

In the voting, election authorities Tuesday invalidated ballots for five parliament seats because of fraud and violence.

The order by Election Commissioner T.N. Seshan meant the election process must start over in five of the 204 constituencies that were at stake in Monday's election.