(CNN) — At least 20 police officers were feared killed Tuesday in a Maoist raid in the Indian state of Chhattisgarh, authorities said.

“Unconfirmed sources tell us 20 policemen have lost their lives,” said Arun Dev Gautam, the state police inspector general.

The morning attack targeted a police security team of about 40 personnel in Sukma district, he said.

Gautam didn’t rule out the use of landmines in the assault believed to involve 200 rebel fighters.

The Maoists ambushed the police team, which included state and armed federal personnel, as it provided security to construction workers, he said.

At a police conference in New Delhi in November, India’s home minister Sushil Kumar Shinde described the rebels as a “major threat” to national security.

At least 97 security personnel and as many guerrillas were killed in Maoist assaults last year, he said.

The rebels, officials say, aim to seize power through an armed liberation struggle.

Since the 1960s, the militants have said they are fighting for the dispossessed.

Authorities suspect that Maoists enjoy support not only in the poorest areas and in tribal communities, but also among youth and intellectuals.

In addition to targeting police, alleged police informers and people they call “class enemies,” the insurgents also attack infrastructure such as roads, bridges, railways, and power and telecommunication networks.

In 2013: Indian politician suffered brutal treatment in Maoist attack