Clashes have broken out in Jordan between anti-government protesters and supporters of King Abdullah II.
The skirmishes followed a demonstration by thousands of people in the capital, Amman, over the government's lifting of fuel subsidies earlier this week.
Some protesters chanted for the king's downfall - a very rare occurrence in the country.
Since the lifting of subsidies, the price of domestic gas has risen by more than 50%.
Diesel and kerosene prices, meanwhile, have increased by a third.
'Playing with fire'
The protests are one of the most serious challenges to King Abdullah's 13-year reign, says the BBC's Dale Gavlak in Amman.
In a largely peaceful protest in Amman on Friday, thousands of marchers near the main Husseini Mosque chanted the Arab Spring slogan: "The people want the downfall of the regime."
But Abdullah loyalists clashed with anti-government protesters near the city's Wasfi al-Tal square on Friday night, with dozens of protesters reportedly being beaten by the king's supporters.
Jordan has mostly avoided the protests that have swept across the region in the past two years, but the decision to raise fuel prices sparked demonstrations.
"Raising prices is like playing with fire," read one banner.
Protests elsewhere on Friday - in the northern city of Irbid and in restive southern towns of Karak, Tafila and Maan - passed off peacefully, reports said.
The subsidy cuts announced by Prime Minister Abdullah Ensour saw the price of gas, used mostly by low-income families for heating and cooking, rise by 54%.
This angered a public already suffering from high unemployment, poverty and inflation.
As the fifth prime minister appointed by the king since the outbreak of protests in Jordan nearly two years ago - following the start of the Arab Spring - Mr Ensour said the measures were needed to reduce a massive budget deficit of $5bn (£3.1bn).
Analysts say the opposition Muslim Brotherhood and its political wing, the Islamic Action Front, may be stoking the flames of dissent in a bid to raise its own profile ahead of the parliamentary elections on 23 January, which it has vowed to boycott.