AFP/Dnipropetrovsk, UkraineExplosions left dozens hurt yesterday in eastern Ukraine in what President Viktor Yanukovych called a challenge to the country ahead of its hosting of the Euro-2012 football tournament.Four blasts went off in central Dnipropetrovsk around mid-day, injuring 27 people including nine children, emergencies officials told AFP, as police combed the city on the Dnieper River for more bombs.Yanukovych vowed a firm response to the unclaimed attack, which came just weeks before the grand European football championship that Ukraine is co-hosting with Poland opens on June 8.“We know that there are victims, we understand that this is another challenge, for the entire nation,” he said while on a visit to a factory in Crimea on the Black Sea.He vowed to punish the perpetrators and anyone plotting “crimes directed at destabilising the situation in Dnipropetrovsk,” though security officials denied yesterday evening that any arrests had been made.Dnipropetrovsk is not a host city in the country’s first major international sports event, but is on the route of the trophy tour that is due there on May 21.The city of 1mn is also the home town of Yanukovych’s fiercest foe, the 2004 “Orange Revolution” leader Yulia Tymoshenko, who is serving a disputed jail sentence that has strained Ukraine’s ties with the European Union.The first bomb hidden in a trashcan near a tram stop exploded at 11.50am (0850 GMT) as a tram was pulling away.“I heard a very loud explosion,” said one witness, a middle-aged woman, who ran after the tram as its doors closed. “Then the tram reopened the doors, and people were jumping out in a panic.”The blast shattered windows in the tram, sending glass shards flying as far as 20m away.Doctors tended to the injured, picking up a woman in her 50s with wounds on her legs from the pavement and loading her into an emergency van.Three more blasts followed over the next hour, all in the same busy part of the city not far from the train station and the Dnieper River. The last explosion was heard at 1pm (1000 GMT).A total of 25 people were hospitalised, officials said.The cellular phone network went down for several hours as ambulances and police in bulletproof vests patrolled the streets, but no panic broke out among the residents, an AFP correspondent observed.Ukrainian prosecutors launched a probe into possible acts of terrorism, with top officials including Interior Minister Vitaly Zakharchenko quickly leaving for Dnipropetrovsk to personally oversee the investigation.No information was released as to the possible perpetrators of the blasts. A similar series of explosions in eastern Ukraine in January last year was linked by officials to an attempt to extort money from the authorities.Europe’s football governing body UEFA said it was confident Ukraine could ensure security despite the attacks, though Donald Tusk, prime minister of co-hosts Poland, said: “This issue needs to be treated with the utmost seriousness.”“This event does not change UEFA’s confidence in the security measures that have been developed by the authorities” to prepare for the sports event,” it said in a statement e-mailed to AFP.The blasts went off as security services were conducting anti-terrorist drills at the Olympic stadium in the capital Kiev, venue for several matches in the Euro-2012 including the final on July 1.