At least 21 Indian police officers have been killed in an ambush in the country's eastern state of Chhattisgarh, officials have said.
Police battled about 300 suspected Maoist fighters - also known as Naxalites - in Rajnandangaon district after a number of officers had been killed in landmine explosions on Sunday, officials said.
Mukesh Gupta, a senior local police official, said that five officers were killed in the first landmine explosion in Rajnandangaon district, about 90km from the state capital, Raipur.
A second mine exploded as police reinforcements reached the scene, killing at least one senior official and possibly more, he told The Associated Press news agency.
N.L. Kanwar, the home minister of Chhattisgarh state, blamed Maoist fighters for the attack and said that helicopters were scouring the area for those responsible.
The Press Trust of India news agency reported that New Delhi was sending 600 paramilitary troops to the area to help with the search.
Sunday's attacks came a month after 11 officers from a special police team were killed after a landmine exploded elsewhere in the state.
The fighters, who say they are inspired by Chinese communist revolutionary leader Mao Zedong, have been battling the government for more than 30 years across more than half of India's 29 states.
They have frequently targeted police and government workers in what they say is a fight for improved land rights and more jobs for neglected agricultural labourers and the poor.
In a statement to parliament last week, Ajay Maken, India's junior home minister, said at least 455 people had been killed in attacks by the Maoists since January this year with Chhattisgarh alone accounting for 148 deaths.
Manmohan Singh, the prime minister, has described the estimated 10,000 to 22,000 Maoist fighters operating in India as one of the biggest threats to the country's internal security.
Last month, the government formally banned the Maoists, officially designating the group as a terrorist organisation.