The Palestinian ambassador to Prague who died in a blast at his residence on New Year's Day was holding the explosive in his hand when it went off, a police spokeswoman told AFP on Monday.
"An experimental blast carried out by experts confirms this theory," Prague police spokeswoman Andrea Zoulova said, denying earlier reports that the blast was caused by a booby-trapped safe.
Jamal al-Jamal, 56, died in hospital on January 1, only three months after taking up his post, following an explosion that occurred soon after he opened a safe.
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"The explosive was not placed on the door or inside the safe and was not there to protect the safe," Zoulova said, adding that the investigation was ongoing.
After the incident, Czech police found 12 firearms at the Palestinian embassy in Prague, including submachine guns and sidearms that were not officially registered in the Czech Republic.
Local media said the weapons were produced in the former Czechoslovakia and supplied to the Palestine Liberation Organisation before communism fell in Czechoslovakia in 1989.
Palestinian diplomats later apologised for hiding the illegal weapons at the embassy.