Communist rebels hijacked a train and briefly held 300 passengers before melting away into surrounding forests in one of a series of attacks in India that threatened to mar elections Thursday in the world's largest democracy.

Much of the violence was focused Wednesday in eastern and central India where communist guerillas have fought for decades for the rights of the poor, but tensions remained high in other regions as the elections exposed ethnic, religious and caste divides in this massive nation of some 1.2 billion people.

The first phase of voting last week saw more than three dozen attacks by Maoist fighters. Violence left at least 17 people dead — including police, soldiers, polling officials and civilians — and three election officials were kidnapped.

On the eve of a second round of voting, several hundred guerillas stopped a train in a show of force and held the passengers hostage for several hours in the eastern state of Jharkhand, where Maoist rebels have vowed to disrupt the elections.

All the passengers were released unharmed and their was no confrontation with security forces, said senior police official Hemant Toppo.

Wednesday's hijacking — which took place in a Maoist rebel stronghold about 560 miles (900 kilometers) east of New Delhi — was one of a series of attacks that included an explosion at another railway station, a blast at a government office, and the slaying of a truck driver in the neighboring state of Bihar.

The rebels have called on the public to boycott the national election and a pamphlet left at the attacked government office described the vote as "a fake exercise."

"Strengthen revolutionary forces. You will pay with your lives if you participate in these elections," it read.

Thursday's vote is the second of five phases of polling that began April 16 and will continue for a month, with results expected May 16. With more than 700 million voters, India normally holds staggered elections for logistic and security reasons.

The rebels, called Naxalites, say they are inspired by Chinese revolutionary leader Mao Zedong. They have been fighting for more than three decades in several Indian states, demanding land and jobs for agricultural laborers and the poor. They generally do not speak to the media and instead communicate through pamphlets or statements sent to newspaper offices.

Tensions were also high in other areas.

In India's troubled northeast, troops were put on alert to prevent ethnic separatists from carrying out attacks.

"We have directed our border guards to remain on heightened vigil," said Assam state police chief G. M. Srivastava after tribal militants ambushed a convoy of trucks in southern Assam on Monday, killing five police escorts and a civilian driver.

In the southern Indian state of Andhra Pradhesh — which has a bitter history of religious and caste violence — more than 60,000 policemen and paramilitary personnel were deployed in areas where polling was to take place.

"We are leaving nothing to chance in ensuring an atmosphere in which the voters will be able to go out and vote freely," said state Chief Electoral Officer I.V. Subba Rao.

Reflecting the myriad differences of India's electorate, few expect a clear winner after a lackluster campaign that has been devoid of resonant, central issues.

Polls indicate neither the Congress party, which leads the governing coalition, nor the main opposition, the Hindu nationalist Bharatiya Janata Party, will win enough seats in the 543-seat lower house of Parliament to rule on their own.

Instead, many of the seats are expected to go to a range of regional and caste-based parties that tend to focus on local issues and local promises, from cheaper electricity for farmers to free color TVs.

That means the elections will likely leave India with a shaky coalition government cobbled together from across the political spectrum — a situation that could leave the next prime minister little time to deal with India's many troubles.