An explosion at the office of Poland's police chief was caused by a grenade launcher - a weapon that had been a gift from Ukraine, he says.

The blast at the police headquarters in Warsaw on Wednesday resulted in police commander in chief Jaroslaw Szymczyk being taken to hospital.

Following the incident, Mr Szymczyk told private broadcaster RMF FM that he had received two of the weapons as a gift from Ukraine.

"When I was moving the used grenade launchers, which were gifts from the Ukrainians, there was an explosion," Mr Szymczyk told RMF FM.

He said he was moving the launchers into an upright position at the time.

RMF cited a source from a Polish delegation that visited Ukraine as saying Mr Szymczyk had received two launchers from officials as presents during visits to the police and the State Emergency Service of Ukraine.

The officials had assured the Polish delegation that the launchers were not loaded, and the delegation took them back to Warsaw by car before leaving them in the back room of Mr Szymczyk's office, the source said.

Sky News has been unable to immediately confirm Mr Szymczyk's version of events.

Mr Szymczyk has been criticised over the incident, with commentators with backgrounds in the security services cited by Polish media as saying that military equipment should not have been taken into Poland from outside the European Union or taken into an office.