Mastermind Fritz Gelowicz told a panel of judges in the western city of Düsseldorf that he and three other defendants had aimed above all to kill as many US soldiers based in Germany as possible.
"That was our very clear intent," Gelowicz said.
He said the group had also targeted US consulates in Germany as "the absolute final warning" to the Berlin government before a key parliamentary vote to pull its troops out of Afghanistan. Gelowicz, on trial since April, could face 15 years in prison for the bid to mount at least three car bombings against US military installations and American citizens in Germany.
Defence attorneys said the men aimed to shorten what had been expected to be a mammoth trial and reduce their sentences by confessing. They have not expressed remorse.
Before the confessions, the trial had been expected to be one of the lengthiest and costliest for a militant plot in Germany since urban guerrillas from the Red Army Faction faced court in the 1970s.
The men are charged with belonging to a terrorist organisation – the Islamic Jihadic Union (IJU) in Pakistan, an extremist group linked to al-Qaida – and plotting to stage attacks with explosives in September 2007.
Gelowicz said he had received three months of terror training in the border region between Pakistan and Afghanistan with IJU instructors and pledged his loyalty to the outfit "with a handshake." He and his fellow defendants spent the past weeks detailing their plans to agents from the Federal Crime Office after suddenly announcing June 9 that they would plead guilty to the charges against them.
Presiding judge Ottmar Breidling said at the start of the hearing that he believed after reviewing the accounts of the confessions that they would lead to a relatively quick end to the trial and expose the dimensions of the plot.
"We are impressed on the one hand by the scope of the testimony and on the other by the candour," he said, noting that the transcripts and notes from the questioning comprised 1,584 pages.
Prosecutors accuse the group, known as the Sauerland cell after the region where they were captured in September 2007, of aspiring to carry out attacks on the same scale as those of September 11, 2001 on the United States which killed more than 3,000 people.
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. The fourth was arrested soon after in Turkey.
Two of the suspects, Gelowicz and Daniel Schneider, 23, are German converts to Islam, a third is a German citizen of Turkish origin, Atilla Selek, 24, and the fourth a Turkish national, Adem Yilmaz, 30.
Prosecutors said they were considering whether to bring charges against a fifth man, a Turkish national living in Germany, Mevlut Kar, who is suspected of providing the group with more than 20 detonators for their explosives.
German media have reported that Kar has ties to Turkish intelligence but federal prosecutor Volker Brinkmann said Monday there was no evidence that he worked as an informant for Ankara.