A series of at least four explosions shook the Ukrainian city of Dnepropetrovsk on Friday afternoon, injuring at least two dozen people in what authorities now suspect were terrorist attacks.

This has been an unprecedented terrorist attack for Ukraine in terms of its scale and level of organization. A series of blasts shook the center of Dnepropetrovsk with an interval of 15-20 minutes, Voice of Russia's Vladimir Sinelnikov said from Kiev.

The authorities have no doubts that it was a terrorist attack. The local police have information that unknown terrorists sent signals to the explosive devices with the help of a remote control system.

The first blast occurred at a tram stop in the center of the city. The bomb was planted in a garbage bin, the Associated Press reported. Other bombs were detonated by a movie theater, a trade school and a park. Bomb-detecting dogs were also sent to the city's main train station.

Interior Minister Vitaly Zakharchenko immediately left Kiev for Dnipropetrovsk to open an investigation.

President Viktor Yanukovych called the explosions yet another challenge for the whole country.

However, Ukraine's opposition party, led by jailed former prime minister Yulia Tymoshenko, alleged that the blasts could have been a government plot to draw attention away from Tymoshenko, whose abuse of power conviction has been condemned by the European Union and Russia.

I don't rule out that the authorities and law enforcement bodies may be among the organizers of a scenario, which involves deflecting the attention of the world and Ukraine from Tymoshenko's case on the whole and her beating in particular, commented deputy parliament speaker Mykola Tomenko.

Friday's attacks were not the first in Dnepropetrovsk, where a bomb planted in a garbage can killed a businessman in November.

Additionally, terrorists were initially blamed for explosions at a shopping center and a building owned by the Makiivuhillia coal company in the city of Makiivka in January 2011.