An unknown explosive device went off on the semi-basement floor of an apartment building in Odessa, southern Ukraine, last night, the Ukrainian state emergency situations service said in a press release.

An unknown explosive device went off on the semi-basement floor of an apartment building in Odessa, southern Ukraine, last night, the Ukrainian state emergency situations service said in a press release.

"No one was killed or injured. However, the blast damaged walls on the semi-basement floor, the ceiling, six windows and six cars", it said.

Police are investigating the explosion as a terrorist attack.

"An explosive device went off early on Thursday morning, damaging two offices located on the semi-basement floor of a three-storey building on Koblevska Street and cars parked nearby. Windows were blown out in several apartments. No one was killed or injured in the blast," an Odessa police spokesman said on Thursday.

Explosives experts, investigators and senior police officers are working at the site. A preliminary examination of the scene established that the explosion occurred inside a commercial organization's office, located on the semi-basement floor of the apartment building.

According to Ukrainian media reports, the blast was staged outside the former office of the Right Sector extremist organization, which is outlawed in Russia.

Recently, Odessa has seen about a dozen explosions, which were staged near volunteer centers, apartment buildings and shops. Some of them are being investigated as terrorist attacks. The last one occurred on February 18. None of these crimes has been solved.

Donetsk rescuers are trying to unblock the Zasyadko mine where 73 workers have been trapped by an explosion, spokesperson for the self-proclaimed Donetsk People's Republic Emergency Situations Ministry Juliana Bedilo said on Wednesday.

The Russian Investigative Committee has extended an investigation against Dmytro Yarosh, a leader of the Ukrainian radical organization Right Sector, accused in Russia of public calls for terrorist and extremist activities.

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