The Maoist guerrillas struck with lightning speed, racing inside the security camp in cars and on motorcycles, spraying the overwhelmed police forces with rifle fire and sending a clear message to the Indian government: back off.

The attack Monday on the remote police base in West Bengal state killed at least 24 police officers and showed that the insurgents are a potent force despite a government crackdown.

"The Maoists have the capacity of launching such attacks at will," said Ajai Sahni, executive director of the Institute for Conflict Management.

The violence highlights the growing power of the shadowy rebel group, which is now present in 20 of the country's 28 states and has an estimated 10,000 to 20,000 fighters.

Prime Minister Manmohan Singh has said India's biggest internal threat comes from the rebels, who have tapped into the rural poor's growing anger at being left out of the country's economic renaissance.

Some local governments in central and eastern India are unable to function because of rebel attacks. The central government and various states launched the "Operation Green Hunt" offensive to flush militants out of the forests.

In response, the rebels have blown up train tracks, attacked railway stations and assaulted railroad employees, Home Minister Palaniappan Chidambaram said.

On Monday, they undertook their most brazen attack ever in West Bengal state.

More than 100 guerrillas raided the security outpost in a blitzkrieg, detonating land mines, setting the facility ablaze, killing two dozen police and stealing weapons, said district magistrate N.S. Nigam.

The attackers rode motorcycles and vehicles into the camp near a bustling market in the village of Shilda, about 105 miles (170 kilometers) southwest of the state capital, Calcutta.

"They first started hurling grenades into the camp and some tents caught fire," one of the survivors of the attack told the Press Trust of India news agency on condition of anonymity. "The sentries opened fire in self-defense, but the Maoists fired from sophisticated weapons as the area plunged into utter confusion."

Police reinforcements scoured the area Tuesday for the assailants, who fled after the assault, Nigam said.

"Never before the police here have suffered so many losses in one attack," Surajit Kar Purkayastha, a police official, said Tuesday.

Kishenji, a top Maoist leader in the area, claimed responsibility in a call to a local television station, saying it was in retaliation for the crackdown.

Chidambaram branded the assault an outrageous challenge to the state.

"Every attack of this kind exposes the true nature and character of the (Maoists)," he said. "Their goal is to seize power. Their weapon is violence. No organization or group in a democratic republic has the right to take to violence to overpower the established legal authority."

But the attacks also exposed the government's inability to seriously damage the rebel group, Sahni said.

"The states, even backed by federal forces, do not really have the capacity to suppress or neutralize these forces," he said.

Troops are spread so thinly on the ground, they are easy targets for the insurgents, he said. If the government does not triple or quadruple its forces, "you will have more and more people being killed on both sides and no significant strategic gains," he said.

Inspired by Chinese revolutionary leader Mao Zedong, the rebels have fought for more than four decades demanding land and jobs for farmers and the poor. About 2,000 people — including police, militants and civilians — have been killed over the past few years.

As India's government has cracked down on the rebels in recent months, it also has said it is ready to discuss all their demands only if they give up violence.

Authorities said Tuesday the crackdown on the Maoists would continue.

"It is a setback because so many lives have been lost. But it will not change our resolve," said Bhupinder Singh, the top police official in West Bengal.