Ukrainian authorities say they have detained two men suspected of orchestrating the late April explosions in the eastern city of Dnipropetrovsk that wounded 31 people.
Interior Minister Vitaly Zakharchenko said the suspects are two men from the city, who had unsuccessfully demanded $4.5 million from authorities for canceling their plans.
He did not elaborate on the suspects' identity or details of their demands.
Four devices placed in garbage bins in Dnipropetrovsk exploded on April 27, injuring passers-by, including nine teenagers.
Some Ukrainian officials have called the blasts terrorist attacks.
The opposition has claimed they could be part of a government plot to divert attention from the imprisonment of opposition leader Yulia Tymoshenko.
Based on reporting by AP and ITAR-TASS