Some 27 people, including nine schoolchildren, were injured as a result of four blasts that hit the city of Dnipropetrovsk in eastern Ukraine around mid-day on Friday, according to Interfax-Ukraine.

Out of the 27 people, 25 have been hospitalized, according to the reports.

Four bombs in trash cans were the source of the blasts. The first blast occurred at a tramway stop in the town center, another near a school and another near a railway station.

Ukrainian President Viktor Yanukovich called the blasts a “challenge,” promising an “adequate response.” Prosecutors have said terrorists might be behind the attack.