Twenty-seven people were wounded by blasts in the Ukrainian city of Dnipropetrovsk, in what authorities are calling a terrorist attack.

Officials say four explosions went off within minutes Friday near a train stop, a movie theater, a park and a downtown area. Some of the bombs were reportedly planted in trash bins.

President Viktor Yanukovich vowed a firm response and said the blasts represent a challenge to the entire country.

Interior Minister Vitaly Zakharchenko quickly left for Dnipropetrovsk to lead an investigation into the attack. Authorities did not immediately release information on the possible perpetrators.

Dnipropetrovsk is the hometown of Ukraine's jailed former prime minister Yulia Tymoshenko, who is serving a seven-year sentence for abuse of office. She is now standing trial on tax-evasion charges that could extend her jail time to 12 years.

Ms. Tymoshenko, an opposition leader, denies the charges and says they are part of a campaign by President Yanukovych to remove his strongest political rival.