Jordanian police said on Saturday investigations showed a homemade explosive device planted near a police van was behind a blast that killed one policeman and injured six others the day before.
Police said on Friday a gas canister stored in the van was behind the blast near a gendarmerie parking lot close to the site of a music festival in the town of Fuheis outside Amman.
"This cowardly act will only increase the determination to do our job to protect people," the interior ministry statement said.
Such incidents are rare, but radical Islamists have long targeted Jordan, a tightly policed country that is also a staunch regional ally of the United States and signed a peace treaty with Israel.