RAIPUR, India (AFP) - The death toll from an ambush by Maoist rebels in central India rose to at least 23 with senior politicians among the victims, a top police officer said on Sunday, in the deadliest attack by the insurgents in over a year.

Saturday's attack was the latest in a long-simmering conflict that pits the militants against authorities in the forests and rural areas of mainly central and eastern India.

"The total number of dead now stands at 23. We can also confirm that 32 people are injured, most of them seriously," state police director general Ramniwas, who goes by one name, told AFP.

State Congress chief Nand Kumar Patel, his son, and former state home minister Mahendra Karma who had set up a controversial anti-insurgent group in 2005 were among those killed in the bomb and gun attack in a remote tribal belt of Chhattisgarh state.

Former federal cabinet minister Vidya Charan Shukla has been airlifted to New Delhi in a "serious" condition, Congress vice-president Rahul Gandhi, who flew to state capital Raipur late on Saturday, told reporters.

The Congress party is the main opposition in the state run by the Bhartiya Janata Party.

Congress chief Sonia Gandhi condemned the incident Saturday as "shocking" and said the party was pained by the attack on its colleagues.

"Naturally we are devastated... It is despicable that ordinary people engaged in political activity were attacked," she told reporters in New Delhi after an emergency meeting with Prime Minister Manmohan Singh.

Dr Singh, who has described the Maoists as the country's most serious internal security threat, urged the state authorities to provide all possible assistance to those who have been injured.

"Such incidents go against the democratic values of our country. Government will take firm action against the perpetrators of violence of any kind," he said in a statement.

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.

Three policemen were killed a fortnight ago when Maoists launched an overnight attack on a state-run broadcaster in Chhattisgarh.

And last week a policeman and eight villagers were killed in a shootout between rebels and security forces.

Eleven policemen were killed in March last year in a landmine blast in western Maharashtra state close to the border with Chhattisgarh.