In court in Düsseldorf, one of the four suspected Islamic militants told the judge he wanted to discuss his intention to confess with the other defendants without legal counsel present. The judge agreed to the request and immediately halted the court proceedings.
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.
"I will submit a full confession and then answer questions," Gelowicz told the court.
"He will submit a confession," a lawyer for Yilmaz said.
Attorneys for Selek and Schneider said their clients would make a "comprehensive" statement largely admiting their role in the plot.
Hearings in the case were suspended until the week of June 22. The lawyers said that between now and then, the four defendants will issue their confessions to agents of the Federal Crime Office.
The trial was expected to be one of the lengthiest and costliest on a militant plot in Germany in decades. But presiding judge Ottmar Breidling said the confessions meant "that the trial will probably be shortened now."
He added that the decision of the defendants to plead guilty could also have a "tangible effect" on their sentences. Based solely on the charges against them, all four could face 15 years in prison if convicted.
The sudden decision to confess was apparently prompted by Yilmaz, who had told relatives during a visit to his prison in the western town of Wuppertal that the evidence against him was so overwhelming that he wanted to put a quick end to the "boring" trial.
The other defendants agreed Tuesday to take a "common line," Yilmaz's lawyer said.
Prosecutors say the group, known as the Sauerland cell after the region where they were detained, aspired to carry out attacks as big 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.