Twenty nine people, including nine children, were injured in four successive bomb attacks that took place on Friday in the city of Dnepropetrovsk, eastern Ukraine, the emergencies ministry said.
According to other sources, there were 10 explosions.
Police later said at least one of the bomb attacks was averted.
A law enforcement source said all of the bombs were homemade without any solid encasement.
“The blast organizers evidently hoped to produce an effect” rather than cause maximum damage, the source said.
Between three and seven people were hurt when an unidentified explosive device went off at a tram stop in central Dnepropetrovsk.
The second blast came about an hour later outside a cinema, injuring seven.
The third explosion took place near a railway terminal and the fourth in a public park.
Several people were hospitalized with fragmentation wounds.
The traffic in the central part of the city has been brought to a standstill.
The Komsomolskaya Pravda v Ukraine daily said there were rumors that several people were killed, but the rumors have not been officially confirmed.
It also said city residents are in a panic.
“Nobody knows where to run, where to hide. People are trying to leave their offices and go home but police are forcing them back into the buildings,” it said.
The RBK-Ukraina agency reported disruptions in mobile communication services.
All of the explosive devices were placed in garbage bins.
No one has claimed responsibility for the attacks.
Police have been put on alert with reinforced details patrolling the city but the authorities said there is no question of introducing a state emergency.
A criminal case has been opened under a “terrorism” statute, the Prosecutor General’s Office press secretary Margarita Velkova said.
Prime Minister Mykola Azarov has ordered the interior minister to head the investigation into the bombings.
President Viktor Yanukovych described the attacks as “yet another challenge for us, for the entire country.”
Similar terrorist attacks took place in the city last fall.