KIEV, December 20. /TASS/. The National Police of Ukraine opened a criminal case over the explosion of a grenade launcher, presented to the Chief Polish Police Commander Jaroslaw Szymczyk during his visit to the country, Ukrainian Deputy Minister of the Interior Yevgeny Yenin said Tuesday.

"The relevant criminal proceeding has been registered in the last few days, which involves a pre-trial investigation and questioning," Yenin told Ukrainian media.

Yenin underscored that Ukrainian policemen "stay in contact with the Polish side to ensure the objectivity of the investigation and to learn relevant lessons to make sure that such incidents never happen again."

The explosion at the police office in Warsaw occurred on December 14. The Polish Ministry of the Interior confirmed that one of two grenade launchers, presented to the Police Commander during his December 11-12 visit to Ukraine by heads of Ukrainian security agencies, exploded. The grenade launchers in question reportedly are anti-tank RGW-90. According to Szymczyk himself, the explosion occurred, when he decided to move the grenade launchers. On Thursday, the Polish Prosecutor’s Office started investigation of this incident.