Dozens of troops and Maoist insurgents have been killed in gun battles in the restive state of Chhattisgarh in central India, police say.
At least 24 soldiers and police and 20 Maoists were killed in jungle clashes, with many police still missing.
The clashes started on Monday as more than 100 troops went to check reports of a rebel camp 500km (310 miles) south of the state capital, Raipur.
"It looks like it was a set-up," a home ministry official told AFP news agency.
Chhattisgarh police chief Vishwa Ranjan said many of the 115 police and soldiers sent to Dantewada district to fight the rebels were still missing.
"A search is now on for our remaining men missing in the area," Mr Ranjan said.
More than 6,000 people have died during the rebels' decades-long fight for a communist state in parts of India.
Prime Minister Manmohan Singh says the Maoists pose the most serious threat to national security in India.
They say they are fighting for the rights of poor peasants and landless workers.
In March, 55 policemen were killed in an attack on a security post, the worst Maoist assault in Chhattisgarh.
The rebels operate in 182 districts in India, mainly in the states of Jharkhand, Bihar, Andhra Pradesh, Chhattisgarh, Madhya Pradesh, Maharashtra and West Bengal.