By Meghana Keshavan

DETROIT (Reuters) - Jury selection began on Tuesday in the trial of seven members of a Midwestern militia accused of plotting to kill police to spark a wider war against the U.S. government.

Calling themselves the Hutaree, the group opposed any government regulation of firearms and explosives and conspired to kill a police officer and then ambush a funeral procession motorcade using homemade explosive devices, a federal indictment unsealed in March 2010 alleges.

The jury in the trial before U.S. District Court Judge Victoria Roberts in Detroit is to remain anonymous to the defendants and public, an unusual measure to protect their safety. Selection could take several days.

Defense attorneys argue the group was merely engaging in angry expressions of free speech in conversations that were secretly recorded and did not demonstrate real intent to carry out acts of domestic terrorism.

No attacks were carried out.

The FBI on Monday warned anti-government extremists opposed to taxes and regulations posed a growing threat to state and local law enforcement officers.

While most convictions were mostly for white-collar crimes -- there were 18 convictions each in 2010 and 2011 and 10 in 2009 -- two Arkansas police officers were shot and killed in May 2010 after an argument with a "sovereign citizen" following a traffic stop.

Another fired at but missed a police officer in Texas last year after a traffic stop.

In the case of the Hutaree, prosecutors contend the group had met regularly since 2008 to conduct military style training and were in training for an impending battle. Federal agents seized machine guns, unregistered short-barrel guns, ammunition, explosive devices and materials that could be used to make explosives, according to court documents.

The charges against all seven include sedition, the attempted use of weapons of mass destruction and firearms offenses. Additional charges were filed against individual defendants.

The seven members of the group facing trial include accused leader David Brian Stone Sr., 47; his wife, Tina Mae Stone, 46; and their two sons, David Brian Stone Jr. and Joshua Matthew Stone. Michael David Meeks, Thomas William Piatek and Kristopher Sickles also face trial.

One group member, Joshua John Clough, pleaded guilty to weapons charges in December. His plea agreement included an admission he was a Hutaree member and that the group's goals included assembling and using explosives against local, state and federal law enforcement officers and their vehicles.

The trial of a ninth member of the group who was indicted along with the others Jacob Ward has been delayed.

The trial was expected to last six to eight weeks.

(Editing by David Bailey and Daniel Trotta)