The Indian government has ordered the NIA to probe Saturday's brutal attacks on a Congress convoy.

The attack, conducted by left- wing Naxalite rebels, left 25 people dead and 32 others injured.

PM Singh, Congress chief and Congress VP have strongly condemned the a"barbaric attack".

The Indian government has ordered the National Investigation Agency (NIA) to probe Saturday's brutal attacks on a convoy of the country's ruling Congress party by left- wing Naxalite rebels in the central state of Chhattisgarh.

The attack left 25 people dead and 32 others injured.

"I have spoken to Raman Singh, the Chief Minister of Chhattisgarh, and he has agreed for probe by the NIA (set up recently to deal with and probe terrorism cases)," Indian Home Minister Sushil Kumar Shinde told the media over phone from New York Sunday.

A group of 250 armed Naxalites ambushed the convoy on Saturday evening at Dharba valley through which it was travelling following a party's campaign rally, wiping out the entire top Congress leadership of the state, including Chhattisgarh's party chief Nandkumar Patel, his son, and local leader Mahendra Karma who had ignited a campaign by locals against the left-wing rebels.

A former Indian Minister, V.C. Shukla, however, survived the attack, but is currently battling for his life at a hospital near the national capital.

Indian Prime Minister Manmohan Singh, Congress chief Sonia Gandhi and Congress Vice President Rahul Gandhi, who met the injured Sunday morning at a hospital in state capital Raipur, have strongly condemned the a"barbaric attack".

"Those who have lost their lives in this barbaric attack are martyrs of democracy. The government will take firm action against the perpetrators of violence of any kind. India will never bow down before the rebels," the Prime Minister said.

Echoing similar sentiments, Sonia Gandhi has described the attack as "shocking". "Naturally, we are devastated. It is despicable that ordinary people engaged in political activity were attacked," she told the media in Raipur.

Even the country's main opposition and the state's ruling Bharatiya Janata Party (BJP) has denounced the attack, saying it was "an attack on India's democracy".

The Naxalites have been operating in at least seven Indian states, including Chhattisgarh and Andhra Pradesh, for the last 40 years. They demand land and jobs for the poor, and want to set up what they claim is a "communist society" by overthrowing the country's "semi-colonial, semi-feudal" government.

The Indian prime minister had earlier described Naxalite insurgency as the country's biggest internal security threat.