Police say at least 13 paramilitary troops have been killed in an attack by Maoist rebels in central India.

R.K. Vij, a top police official in Chhattisgarh state, says the attack took place Monday in Sukma district, 385 kilometers (240 miles) south of Raipur, the state capital.

Few other details were immediately available from the remote region.

The rebels have been called India's biggest internal security threat. They operate in 20 of India's 28 states and have thousands of fighters, according to the Home Ministry.