Security agents in Jordan were interrogating 130 demonstrators who could face charges for calling for the downfall of U.S. ally King Abdullah in protests triggered by a sharp rise in fuel prices.
Judicial officials told Reuters on Sunday the young men, many of them in their teens, had been detained for 15 days and could be charged with threatening the state.
The men were among dozens arrested during protests that began on Wednesday in impoverished towns across the kingdom and in many places turned violent.
"These are prisoners of conscience who should be released," said Musa Abdallat, a prominent human rights lawyer.
Unemployed youths attacked police stations, closed roads with burnt cars and torched government buildings. One protester was killed. A large protest on Friday in the capital Amman passed off largely in peace.
The opposition is keeping pressure on the government to reverse fuel price hikes, but Prime Minister Abdullah Ensour said on Sunday the government would not change course.
Some of the men in detention were among thousands who chanted the Arab Spring slogan "the people want the downfall of the regime" near the Husseini Mosque in downtown Amman.
Jordan has so far largely avoided the unrest that has swept across the Middle East over the past two years, but the decision to lift fuel subsidies sent thousands on to the streets.
Instability in Jordan would come at a dangerous time for the region, when Syria's war risks spilling across borders and Israel is bombing Palestinians in Islamist-run Gaza.
The judicial officials said those detained could be charged with "threatening to undermine the regime, illegal gathering, and creating civil strife."
Although the charges carry sentences of up to five years, convictions in such cases are rare. Dozens of protesters arrested for insulting Abdullah during smaller Arab Spring-inspired demonstrations were pardoned.
"They have been arrested to put pressure on them to retreat from their stances. Putting them in prison for their political views only leads to more frustration," said Abdallat.
The chants against Abdullah were an escalation in demands by Jordan's tribes, the kingdom's original inhabitants that form the backbone of support for the ruling Hashemite dynasty. The tribes depend on state perks and have been angered by the austerity moves that would cost them privileges and state jobs.
Despite recent frustrations, many Jordanians still see Abdullah, a friend of the West, as a bulwark of stability, balancing the interests of native tribes and the increasingly assertive Palestinians in Jordan, who now outnumber the tribes.
While street protests have subsided, strikes organised by some of Jordan's unions representing engineers and teachers have kept pressure on the government.
The Muslim Brotherhood, Jordan's largest opposition movement, appealed on Sunday to Prime Minister Ensour to either freeze or rescind the price increases and called for detainees to be released.
"The country's stability should be a bigger concern than enforcing the price rise. It's clear your decision was based on fiscal considerations and did not take into consideration its political and social impact," the Islamic Action Front, the political arm of the Brotherhood, said in a letter to Ensour.
"It has become clear that our warning to you that moving ahead with the lifting of subsidies would have grave consequences for the county did not turn out to be an exaggeration," the letter said.
But Ensour said in published remarks "retreating from the move would lead to worse results than protests and sit-ins."
Ensour said the price increases, part of an austerity programme aimed at securing a $2 billion loan from the International Monetary Fund, had averted a fiscal crisis next year.
(Reporting by Suleiman Al-Khalidi; Editing by Rosalind Russell)