RANCHI, INDIA - Maoists shot dead two mine officials and blew up railway tracks in India's east on Monday, reacting to an imminent government offensive against the rebels who are seen as the country's biggest internal security threat.

The rebels have ignored repeated calls to renounce violence and negotiate and stepped up their attacks in recent past months, prompting the government to go after them in a concerted strike.

The timing of the government offensive is not yet known but is expected later this month. Apart from addressing a massive security issue, the government aims to free mineral-rich areas worth billion of dollars now under rebel control.

The rebels have vowed to fight government forces and called a two-day strike on Monday, attacking bridges and railway tracks in the eastern state of Jharkhand.

They also gunned down two officials of a private mining firm, underlining the risks of doing business in rebel-held areas where extortion, abduction for ransom and intimidation are common.

"Panam Coal Mine director Sheetal Prasad and additional director Dinanath were taking a morning walk when the rebels gunned them down," senior police official M L Meena said.

Police said they were investigating if the officials were killed because they had refused to pay the rebels.

Maoists also injured three passengers of a bus they fired on early on Monday in a bid to enforce the strike.

"The rebels (also) torched three trucks," R K Dhan, another senior police official, told Reuters by telephone.

The strike comes days after the rebels killed 17 policemen in western Maharashtra state. Last week they beheaded a police officer in Jharkhand.

The Maoist rebellion began four decades ago championing the cause of poor peasants in the east, but has now spread to about 20 of India's 29 states, with the rebels targeting police and government property in hit-and-run attacks.

India's cities and bigger towns are largely free of the violence, but Prime Minister Manmohan Singh has warned the rebels had managed to retain support among a cross-section of society. --REUTERS