NEW DELHI, June 1 (Xinhua) -- At least two para-military troopers were injured in a blast triggered by left-wing rebels in the central Indian state of Chhattisgarh Friday, police said.

The explosion took place at Aranpur in the state's Dantewada district.

"The troopers of the Central Reserve Police Force (CRPF) were on a routine patrol when Naxalites triggered the improvised explosive device (IED) blast. They have been admitted to a government hospital, where the condition of one is said to be serious," a police official said.

Chhattisgarh is among the seven Indian states hit by Naxalite violence. This is the second attack on security forces by the rebels in the last 10 days. Six troopers were killed in a similar attack in the district on May 20.

The left-wing rebels say they are fighting for land rights for tribal people and the rural poor. Their insurgency began in the eastern state of West Bengal in late 1960s, spreading to more than one-third of India's 600-plus administrative districts.

Though major offensives by security forces in recent years have pushed the rebels back to their forest strongholds and the levels of violence have fallen, hit-and-run attacks are still common, killing hundreds of people, mostly security personnel, every year.

Former Indian Prime Minister Manmohan Singh had described Naxalite insurgency as India's "greatest internal security threat."