NEW DELHI, India (CNN) -- Divers spent Monday searching for 36 members of an anti-insurgency unit who went missing after Maoist rebels fired on and sank their boat in eastern India, state media said.
The patrol boat, carrying 64 members of the police squad, came under heavy fire in a reservoir in the state of Orissa, the Press Trust of India reported.
Twenty-eight people swam to safety. The rest remained missing Monday.
Officials have not recovered any bodies from the 40m (130 ft) deep reservoir.
The squad was part of the Greyhound force, set up to fight Maoist rebels -- known as 'Naxals' -- in Orissa and Andhra Pradesh state.
The rebels, who claim to be fighting for the poor and the dispossessed, have been battling police in an insurgency that began in the late 1960s and has resulted in thousands of casualties.
Indian Prime Minister Manmohan Singh has called Naxalism India's biggest security threat. Last year, more than 800 people were killed in Naxal-related violence across the country, according to local media reports.