AMMAN (Reuters) - Thousands of demonstrators chanted the Arab Spring slogan "the people want the downfall of the regime" in Jordan on Friday, although a day billed as the culmination of three days of occasionally violent protests passed off largely in peace. The staunch U.S. ally has so far largely avoided the street unrest that has swept across the Middle East over the past two years, but a decision this week to raise fuel prices led to demonstrations that raised the specter of long-term instability. The mainly urban Muslim Brotherhood announced on Friday it was joining the protests, lending the voice of the country's largest opposition movement to demonstrations which had previously mainly been focused on rural and tribal areas. "Go down Abdullah, go down," the main crowd of about 3,000 protesters chanted as police, some in riot gear, largely stayed away from crowd. "Raising prices is like playing with fire," said one banner. Witnesses said other Friday protests also ended peacefully in the northern city of Irbid and in restive southern towns of Karak, Tafila and Maan, dispelling fears of wider civil unrest. "The government succeeded in frightening people of chaos and many people were discouraged by what they see as the alternative, as chaos," said Lamis Andoni, a political analyst. Protests had turned violent in impoverished towns across the kingdom since Wednesday when the government imposed a hike in the price of fuel. One protester was killed on Thursday as a crowed tried to storm a police station in Irbid. Most of the civil unrest has taken place in outlying areas inhabited by tribes, Jordan's original inhabitants who now form a minority outnumbered by Jordanians of Palestinian origin. The tribes supply the army and security forces with recruits and form the backbone of support for the ruling Hashemite dynasty. They are seen as wary of the prospect of democratic reforms that would cost them privileges and state jobs. The Brotherhood are rivals to the tribes for power, and their decision to back protests signaled discontent spreading, although senior Brotherhood figures did not appear in person. A friend of the West, the monarch is seen by many Jordanians as a bulwark of stability, balancing the interests of native tribes and the increasingly assertive Palestinian majority. Abdullah accepted constitutional changes in August that devolved some of his powers to parliament, paving the way for a prime minister emerging from a parliamentary majority rather than one handpicked by him. However, urban politicians say he has been constrained by the tribes and slow to adopt reforms.