Indian officials have expressed outrage over an attack by Maoist rebels on a convoy of ruling Congress party members that left at least 23 people dead.
Saturday's attack targeted the politicians as they left a campaign event in the eastern state of Chhattisgarh.
Congress Party Chief Sonia Gandhi denounced the ambush as a "cowardly attack".
Gandhi arrived in the state capital, Raipur, Sunday, along with Prime Minister Manmohan Singh to visit the dozens injured. Both vowed that the government will take firm action against those responsible for the attack.
Police say the rebels triggered a landmine on Saturday afternoon before opening fire on the convoy of Congress Party workers in the densely forested Sukma area of Chhattisgarh state.
Among those killed was state party official Mahendra Karma, who founded a local militia (Salwa Judum) to combat Maoist rebels. Also killed were state Congress party chief Nand Kumar Patel and his son. The Congress party is the main opposition party in the state, which holds elections later this year.
The rebels have been fighting the central government for more than four decades, demanding land and jobs for tenant farmers and the poor.
Thousands have been killed in their insurgency.