The Ukrainian Interior Ministry warns against disrupting the negotiating process between the government and the opposition and dismisses accusations that government officials could be responsible for provocations.

"After yesterday's explosion, the Euromaidan commandants have once again accused someone of provocation, saying that the explosives had been smuggled to the Trade Unions House in a box inscribed as 'medicine'. However, this theory evokes some questions. In particular, who could have gotten to the fifth floor but members of the right-radical organization themselves, which they are guarding heavily? And it's also hard to understand why medicine should be brought to the fifth floor where Right Sector activists are staying, while the medical ward is at a different place?" the Interior Ministry said in a statement on Friday.

"The incomprehensible position of the commandants of the seized buildings causes questions. They decided on their own not to let police officers into the buildings to examine the scene and collect the necessary material evidence," it said.

"There is another thing: a kind of regularity with which various high-profile incidents happen around Euromaidan. It has become a trend that some incidents involving participants in mass unrest happen at the end of a week, which serves as formal grounds to gather for another assembly," it said.

"The Ukrainian Interior Ministry stresses that armistice and a negotiating process at the Verkhovna Rada between the government and the opposition are continuing. They must not be violated in any way so as not to provoke new mass unrest," it said.

It was reported earlier that an explosion in the Trade Unions House on Thursday injured a man, who was taken to city hospital No. 17 in critical condition.

Doctors said the man, who had been on the fifth floor of the Trade Unions House, was opening a box inscribed as 'medicine' when it blew up, injuring him. It was reported later that one more person had been injured.

Channel 5 television reported on Friday that Roman Dzvinsky, who opened the box, had his fingers torn off, and the other victim, Nazar Derzhylo, 15, lost an eye.

Activists camping on Independence Square in Kyiv, known as Maidan, prevented an investigative team from reaching the scene of the blast, and a number of parliamentarians and activists also barred investigators from meeting with the victims in the hospital.

Valeriy Mazan, an acting chief of the Kyiv city police department, said a criminal case had been opened into the incident on charges of "careless storage of firearms or ammunition."