NEW DELHI: India's chief anti-terrorism agency will investigate a weekend Maoist rebel attack that killed 24 people including top local politicians, the deadliest strike in three years, officials said on Monday.

A team from the National Investigation Agency, created after the 2008 Mumbai attacks to investigate terror-related crimes, will head to the site of Saturday's attack in the central state of Chhattisgarh, officials said.

“I have asked the NIA to launch a probe. The buck has to stop somewhere,”junior home minister RPN Singh told reporters.

Hundreds of heavily-armed rebels ambushed a convoy carrying local leaders of India's governing Congress party as it travelled through the forested Sukma area, about 345km from the state capital Raipur.

They blocked the road by felling trees before detonating a land mine and opening fire, police said.

Congress chief Sonia Gandhi, who rushed to Raipur along with Prime Minister Manmohan Singh after the ambush, condemned what she called a “cowardly act” by the Maoists.

An official with the NIA said on condition of anonymity that the rebels took advantage of lower than normal levels of security for the convoy.

“We will investigate every aspect of the latest attack. The rebels used sophisticated weapons in the attack to target politicians. Their security was not handled seriously by the local cops,” the official told AFP.

The attack was the latest in a decades-long conflict that pits the insurgents against authorities in the forests of mainly central and eastern India.

State Congress chief Nand Kumar Patel, his son Dinesh, and former state home minister Mahendra Karma -- who had set up a controversial anti-Maoist militia group in 2005 -- were among those killed.

Maoist rebels, who have been described by prime minister Singh as the country's most serious internal security threat, have been fighting since 1967.

They demand land and jobs for the poor, and want to establish a communist society by overthrowing what they call India's “semi-colonial, semi-feudal”form of rule.

The revolt is believed to have cost tens of thousands of lives.

In April 2010 a rebel assault killed 76 policemen in the state, where the Congress party is the main opposition.

In 2009 government forces launched a huge anti-Maoist offensive known as “Operation Green Hunt”, but the often poorly-trained police have had to contend with a deadly series of attacks.

Critics believe attempts to end the revolt through security offensives are doomed to fail, saying the real solution is better governance and development.