In what authorities call one of their biggest terror cases in decades, three Germans and a Turkish national face charges of belonging to a terrorist group and conspiring to mount a series of devastating bombings in German cities.

“They were determined to exterminate the enemies of Islam, in particular Americans and American institutions,” federal prosecutor Volker Brinkmann told the court. “The attacks were to be on the scale of the September 11, 2001 attacks.”

Prosecutors say the four are hardened members of the Islamic Jihad Union, an extremist group with roots in Uzbekistan and ties to Al-Qaeda which is believed to have set up militant training camps along the Pakistan-Afghanistan border.

The defendants are accused of planning to car-bomb US institutions in Germany and nightclubs popular with Americans. Authorities said the men had planned bombings between early September 2007 and mid-October 2007, when the German parliament was to vote to extend

participation in the NATO peacekeeping force in Afghanistan. They were captured in September 2007.

Their aim, authorities say, was a deadly bombing “of unimaginable size,” according to chief federal prosecutor Monika Harms, which along with targeting Americans would also punish Germany for its military presence in Afghanistan.

Attorneys for the four defendants said the state’s case was based in part on testimony by inmates in countries such as Uzbekistan and Kazakhstan who may have been subjected to torture.

“That endangers not only the prisoners… but also the rights of the accused to a fair trial,” lawyers Dirk Uden and Hannes Linke said in a statement presented in court.

Security was extremely tight around the courtmhouse in this city in western Germany, with long lines at airport-style checkpoints, and the four bearded defendants separated from the five-judge panel by bullet-proof glass.

German media have called it the biggest terror trial since urban guerrillas of the Red Army Faction answered to murder charges in the 1970s. It could last two years and the defendants could face 15 years in prison.

The so-called Sauerland terror cell was named after a region east of Düsseldorf where authorities captured the suspects nearly two years ago along with 26 detonators and 12 drums of hydrogen peroxide.

After months of surveillance, police using US and German intelligence said they caught three of the suspects red-handed, mixing chemicals to make the equivalent of 410 kilogrammes (900 pounds) of explosives – 100 times the amount used in the 2005 London bombings that killed more than 50 people. A fourth suspect was extradited from Turkey to Germany last November.

Two of the suspects, Fritz Gelowicz and Daniel Schneider, are German converts to Islam; a third is a German citizen of Turkish origin, Attila Selek, 24, and the fourth a Turkish national, Adem Yilmaz, 30. The cases of Gelowicz, 29, and Schneider, 23, have particularly shaken the

country, raising questions how seemingly “normal” Germans could convert to a radical brand of Islam and plan attacks on their home soil.

Yilmaz sparred with the judges Wednesday, at first declining to remove his white knit skullcap, then repeatedly refusing to stand before the court.

“There is only one for whom I will stand – Allah,” he said.

The prosecution has built its case around vast records of wiretapped conversations and e-mails in which the cell discussed its plans.

In one exchange, a suspect asks the amount of hydrogen peroxide solution required to kill an American: “How many grammes do you need to blow him to bits?”, according to prosecution evidence.

A man believed to be Schneider responds: “If you pack it in steel, 20 grammes, 30 grammes. Then he’s dead.”

Germany, which opposed the 2003 US-led invasion of Iraq but has around 3,700 troops in Afghanistan under NATO command, has beefed up security and surveillance in response to the threat of militant attacks.