Jordan has been hit this week by the worst unrest since the beginning of the Arab Spring in early 2011, with calls for King Abdullah II's ouster.
The protests came in the wake of Prime Minister Abdullah Ensour's announcement Tuesday that fuel prices would be increased, affecting Amman and 12 other cities across Jordan.
At least 14 people were reported injured and 35 people arrested in clashes that included the assaults on government buildings and the torching of cars and gas stations.
"Revolution, revolution, it is a popular revolution," a crowd of more than 2,000 people chanted in Amman's main square outside Jordan's Interior Ministry, King Abdullah II, a U.S. ally. "Freedom is from God, in spite of you, Abdullah."
Riot police in Amman used water cannons to disperse some of the protesters.
Protesters armed with assault rifles attacked a government building in Maan, a hotbed for Islamic militants located 150 miles south of Amman, after noon prayers, opening fire and wounding police officers who tried blocking them, according to official reports.
While in the city of Karak, eyewitnesses and police say protesters marched through the streets chanting: "Down, down with you, Abdullah," and "Get out and leave us alone" as they shattered shop windows.
The protests were not "spontaneous," but triggered by the Muslim Brotherhood, a Jordanian security official told the Washington Post.
"The Muslim Brotherhood had a plan, and they were well-organized. For them, it is a gift from heaven," the official said.
Jordan had been largely been spared the upheaval that has hit other nations in the region in spite of discontent over corruption and worsening economic conditions.
"Although it is already winter, the Jordanian spring is about to begin," Mohammed Husseini, 25, an Islamist protester said.
The Muslim Brotherhood held a demonstration calling for democratization and the weakening of the king's power that drew 10,000 people last month.
Abdullah has called for new elections on Jan. 23, but the Brotherhood and other opposition groups have vowed to boycott them.