Nine members of a rightwing Christian militia in the US were charged yesterday with plotting to murder a policeman and then bomb his funeral in an attempt to provoke an anti-government uprising.

Eight of the Michigan-based group, which includes one woman, were arrested at the weekend in raids in three states, amid warnings from civil rights groups of a surge in the number of extremist militias and "patriot" organisations that see the government as the enemy. A ninth person remained at large as charges of sedition and the planned use of weapons of mass destruction were issued.

The members of the group, called Hutaree, allegedly planned to kill the policeman and plant improvised bombs – modelled on those used by insurgents in Iraq – along the route of his funeral, to murder other officers and mourners.

Hutaree, which the group says means Christian warrior, is described by prosecutors as advocating attacks on law enforcement agencies as the "foot soldiers" of the federal government.

"This is an example of radical and extremist fringe groups which can be found throughout our society," said Andrew Arena, the FBI agent in charge of the investigation in Michigan. "The FBI takes such extremist groups seriously."

Hutaree describes its doctrine as based on the testimony of Jesus and warns of a looming battle with the antichrist. "The Hutaree will one day see its enemy and meet him on the battlefield, if so God wills it," the group says in its literature.

Among the forums on the group's website is one dealing with weapons, and another called the "evil Jew forum".

According to prosecutors, the accused Hutaree members spent 18 months planning the killings. After attacking the funeral, militia members planned to retreat to fortified sites and begin a war against the government. The prosecution says the attacks were intended to "intimidate and demoralise law enforcement".

"It is believed by the Hutaree that this engagement would then serve as a catalyst for a more widespread uprising against the government," the indictment said.

Prosecutors say the accused conspirators were led by David Stone, 45, known as Captain Hutaree. He is alleged to have used the internet to find information on improvised bombs in Iraq and to have told his son to obtain the materials. The prosecution also alleges that Stone taught Hutaree members to make bombs.

Stone's former wife Donna was among those arrested. One of his sons, Joshua, is the ninth person being sought by police.

Last month, a prominent civil rights group warned of a surge in the number of anti-government extremist groups and armed militias, driven by deepening hostility on the right to Barack Obama, anger over the economy, and the increasing propagation of conspiracy theories.

The Southern Poverty Law Centre identified Michigan as one of the states with the highest number of rightwing militias and extremist "patriot" groups. The number of such organisations rose by nearly 250% to more than 500 last year.

The centre said police officers were a favoured target of extreme rightwing groups, with six murdered by militias since Obama became president.

The Conservative Political Action Conference this February was cosponsored by groups such as the John Birch Society, which believes Dwight Eisenhower was a communist agent, and the Oath Keepers, which suggests that the government has secret plans to declare martial law and intern "patriotic Americans in concentration camps," the SPLC said.