KIEV - An extensive investigation is underway into what Ukrainian prosecutors believe is a terrorist attack, after four bomb blasts rocked Dnepropetrovsk city in eastern Ukraine Friday afternoon.

A regional prosecutor's office has started criminal proceedings on charges of terrorism over the blasts, which injured at least 27 people.

A damaged tram is seen at the scene of an explosion in Dnipropetrovsk, April 27, 2012. [Photo/Agencies]

Deputy Head of Ukraine's Security Service (SBU) Vladimyr Rakitskiy meanwhile said the SBU was not considering the introduction of a national emergency over explosions.

Home-made bombs planted in garbage cans were the cause of the explosions, Rakitskiy said.

The security official said the SBU woould work with the prosecutors to investigate the resonant case, adding no suspects had been detained yet.

The explosions in Dnepropetrovsk come ahead of the Euro 2012 football championship, which Ukraine is co-hosting with Poland this summer.

Following the blasts, Ukrainian President Viktor Yanukovych said the explosions were a challenge for the whole country, adding that a special investigation team would be set up to investigate the explosions.

According to the country's Interior Ministry, 25 people, including nine children are currently being treated in hospitals following the blasts. Twenty of them have fragmentation wounds, four are in satisfactory condition and a 16-year-old girl remains in serious condition with lacerations to her face.

Two of those injured refused admission because their wounds were not serious, the ministry said.

The bombs went off within an interval of one and a half hours, beginning from 11:50 am local time (0950 GMT) at a busy streetcar station. The other bombs exploded near the central cinema, in front of Globa Park and near the city Opera, the city's most crowded places.

Dnepropetrovsk region authorities have banned public events until May 2. 

People assist an injured woman at the scene of an explosion in Dnipropetrovsk, April 27, 2012. [Photo/Agencies]