Maoists killed 17 people, including the son of former Jharkhand chief minister Babulal Marandi and two women, and wounded four others in a pre-dawn attack at Chilkhadih village in Giridih district on Saturday.
"Armed Naxalites opened fire during a cultural programme between 12.30 am and 1 am and killed 17 people, including Anup Marandi, the son of former chief minister Babulal Marandi," said Deputy Inspector General of Police R K Mullick.
The injured were rushed to Giridih hospital, he said.
Condemning the attack, Jharkhand Chief Minister Madhu Koda said, "It is a sad incident. Such attacks are in retaliation of police action against them. In the last few months, the police has arrested a number of Naxals and destroyed their bunkers and training camps."
Koda said he has spoken to Marandi and he will visit the village.
Marandi's brother Nunulal, who was also present at the function, escaped unhurt.
The armed Naxals mingled with the crowd that had gathered to watch the the cultural programme before they attacked, Additional Superintendent of Police (Giridih) Arun Kumar Singh said.
The programme was organised as part of a local football match that was held on Friday afternoon.
Singh admitted to lapses by the police in the shootout. Virendra Singh, the in-charge of Deori police station which has Chilkhadih within its jurisdiction, was deputed along with police personnel for the football match and cultural programme. But he returned on Friday evening after the prize distribution ceremony.
"It is a clear case of negligence on the police officer's part," Singh said.
The attackers could have fled to neighbouring Bihar as the village was on the border between the two states, he said.
Jharkhand Director General of Police V D Ram has rushed to the spot and an intensive search and combing operation has been launched by the police from both states.
Marandi said he had received the information that his son was among those killed in the incident, in which some attackers were dressed in Central Reserve Police Force uniforms.
"My family is a target of Naxalites. My son and brother should not have ventured out at night," he said.
Marandi alleged that there was an increase in Maoist violence in Jharkhand and said the Chilkhadih incident was another episode in a series of Maoist attacks.
"Neither the Jharkhand government not the Centre has any policy to curb Naxals or bring them to the mainstream. The Naxals have spread their tentacles in all districts of thestate and 156 districts in the country," said Marandi, who represents Koderma Lok Sabha constituency and heads the Jharkhand Vikas Morcha (Democratic).
The attack was similar to the killing of former Jharkhand Mukta Morcha member of Parliament Sunil Mahto on March 4 this year. Naxals had killed Mahto during a football match organised to mark Holi at Bagudia village in East Singhbhum district.