NEW DELHI - Indian Prime Minister Manmohan Singh and the ruling Congress party have condemned the horrific attack on party leaders by left-wing Naxalite rebels in the central state of Chhattisgarh, in which at least 17 people were killed and more than 20 others injured.

A group of armed Naxalites Saturday ambushed a Congress party convoy at Dharba Valley in the state ruled by the country's main opposition Bharatiya Janata Party (BJP), killing 17 people on the spot and abducting a senior leader along with his son, according to a senior police official.

"All the injured, including former central Minister and senior Congress leader V.C. Shukla, are currently being treated in various hospitals," he said, on condition of anonymity.

The prime minister has strongly condemned the horrific attack and offered all kinds of assistance to state Chief Minister Raman Singh. He is due to visit the injured Sunday.

Congress party chief Sonia Gandhi has described it as "an attack on democracy" while her son and party vice president Rahul Gandhi is currently camping in state capital Raipur. "The Congress party stands by the families of the victims," he told the media.

Meanwhile, local Congress workers have staged demonstrations throughout the night in Raipur and called a 24-hour closedown of Chhattisgarh to protest against the state government's inadequate security arrangements for the Congress leaders who were ambushed while returning from a political rally.