A series of bombings in the Ukrainian city of Dnipropetrovsk fanned security fears over the weekend as the nation prepared to host a major soccer tournament.

The Friday blasts injured at least 27 people, officials said. They began around noon and targeted a tram stop, a theater and a railway station in the eastern Ukrainian city of more than 1 million people.

Authorities said there were at least four blasts, while others reported as many as 10 explosions.

City authorities offered rewards for information leading to the identities of those responsible for the bombings, which the government is treating as acts of terrorism.

Ukrainian President Viktor Yanukovych said Saturday in the Crimea the bombings were "a challenge for the whole country," adding the "best detectives from both Dnipropetrovsk and Kiev" were sifting through the evidence, Ukrainian National Radio reported.

The national prosecutor general's office said investigative teams from regional law enforcement agencies were working at the scene and that the Dnipropetrovsk regional prosecutor had opened a criminal case.

Health officials reported 22 people remained hospitalized over the weekend, with four in serious condition but none with injuries considered life-threatening.

Saturday also saw the arrival in Dnipropetrovsk of Andriy Klyuyev, head of Ukraine's National Security and Defense Council, the broadcaster said.

Although some analysts were skeptical of a direct link between the bombing and this summer's Euro 2012 European Football Championships to be co-hosted by Ukraine and Poland, security fears surrounding the event were already high and the Dnipropetrovsk blasts only intensified them.

Euronews reported a feeling of general insecurity had spread through the city and that Kiev was attempting to keep panic from spreading to other regions before the June tournament.

The government in March emphasized it is working with NATO on providing security for the championship tournament of the Union of European Football Associations, to be played throughout the month at sites in Ukraine and Poland and ultimately leading up to the July 1 final at Kiev's Olympic Stadium.

UEFA, which has already taken criticism that Ukraine isn't prepared to host the event, issued a statement saying the blasts won't change its plans.

While awaiting the results of the investigation, the soccer body asserted, "This event does not change UEFA's confidence in the security measures that have been developed by the authorities in view of UEFA Euro 2012, and which will ensure a smooth and festive tournament."

Speculation if the bombings were specifically meant to disrupt the tournament was mostly dismissed by Ukrainian analysts, the Voice of Russia reported.

Dnipropetrovsk, they noted, isn't a host city for the event, unlike the cities of Kharkiv, Lviv, Kiev and Donetsk, which weren't targeted.

Yanukovych's political opponents claimed the blasts were the work of the Ukrainian secret services, which, under their theory, are trying to sow instability as a pretext to crack down on dissenters and hand the police more power.

But Kirill Frolov, head of the Institute for CIS Studies' Ukraine Department, told the Russian broadcaster this was also unlikely because Yanukovych and his Party of Regions are committed to seeing the tournament come off without a hitch as a matter of national prestige.

"He does not need those explosions, even politically, because the European football championships have been the Party of Regions' key pre-election slogan," Frolov said.