"The two men have admitted the facts and described the circumstances of their campaign," Elzbieta Czerepak, spokeswoman for the prosecutor's office in the southwestern city of Wroclaw, told AFP.
The men, who due to reporting restrictions can be identified only as Adam K. and Mikolaj G., are both 38.
Czerepak said they acted out of a desire for material gain.
After they were arrested in early October, Polish police said the men were suspected of having tried to extract a €6 million ($8 million) ransom from Ikea in exchange for calling off their campaign.
Booby-trapped alarm clocks blew up at Ikea stores in Belgium, France and the Netherlands on May 30th, while a blast in the kitchen equipment department of a store in Dresden, Germany, reportedly left two customers needing hospital treatment on June 10th.
On September 2nd police evacuated two stores in the Czech Republic, defusing a booby-trapped device found near one of them.
Adam K. has been identified as a former manager for several leading firms, with solid multilingual, technical and IT skills.
Mikolaj G., meanwhile, has a record for drug trafficking.
The two men risk up to 12 years behind bars if found guilty, according to Czerepak.