CALCUTTA, India -- The ringleader of a Hindu mob that burned an Australian missionary and his two sons alive was sentenced to death on Monday, as heavily-armed police guarded churches and clerics against a possible backlash.

Tight security surrounded the court in Bhubaneshwar, the capital of Orissa state, as it handed down the sentence for Hindu activist Dara Singh and jailed 12 accomplices for life.

They were convicted last week of attacking Graham Staines and his sons, Philip, 10, and Timothy, 6, as they slept in their jeep in an isolated village and then setting the vehicle afire. The incident four years ago was part of a wave of attacks on Christians blamed on Hindu radicals fighting conversions, and underscored underlying tensions between India's mainly Hindu population and its religious minorities. "The court has given the death sentence to Dara Singh," K. Sudhakar, a lawyer for the Central Bureau of Investigation, told reporters outside. "This is a good judgment and it will increase public faith in the judicial system."

India inherited the penalty of death by hanging from British colonial rule but uses it only rarely and only for the worst cases. A state high court must endorse the trial court ruling.

Only about 40-45 people have been hung in the past three decades and the appeal process, going right up to the Supreme Court and the president, can take several years.

Singh is expected to appeal both his conviction and sentence.

He had become a popular activist and was seen as something of a hero -- supporters formed their own "Dara's Army" -- prompting fears the tough penalty could spark a backlash in Orissa.

"We have deployed armed police to prevent any fallout of the verdict," said Yogesh Bahadur Khurania, superintendent of police in Mayurbhanj district where Staines' widow, Gladys, has stayed on with her daughter to run a home for lepers. "We are providing security outside churches, and giving security officers to Christian fathers," Khurania added.

Hindu political groups deny supporting Singh, a petty criminal from India's most populous state, Uttar Pradesh, who made a name for himself as a Hindu activist in Orissa.

But they accuse Christian missionaries of tricking poor Hindus and tribal people into converting with promises of money and other benefits. Missionaries deny that and insist all conversions are voluntary.

While condemning the killings, some Hindu hardliners say they are a reaction to these so-called forced conversions.

Some critics say Hindu extremists have been emboldened by the rise to power of the Hindu nationalist Bharatiya Janata Party, which leads the federal coalition government.

They say campaigns against the Westernizing influence of Christian missionaries help stir up resentment against all minorities, often exploding into violence against the bigger Muslim community.