Jordan's King Abdullah II dissolved parliament and called early elections on Thursday, the royal palace announced on the eve of a major rally by the Islamist opposition to demand reforms.
"The king has decided to dissolve the chamber of deputies from this Thursday and to call early elections," a statement said. It gave no date, but the monarch has said he wants polls to be held by the end of 2012.
The opposition Muslim Brotherhood said earlier it was going ahead with its planned rally in central Amman on Friday by an estimated 50,000 supporters.
A demonstration in support of the king was called off over fears of unrest as it would have coincided with the Islamist rally, organisers said.
"We have postponed indefinitely our demonstration scheduled at the same time as the Muslim Brotherhood's to avoid any problems," said Jihad al-Sheik, head of an Internet-based youth group that organised the event.
The cancellation came "after a request to that effect from the director of general security, Hussein al-Majali, MPs and tribal leaders" to prevent unrest.
Around 200,000 people had been expected to turn up at the demonstration in Amman to show their support for the king's efforts to bring in reforms.
Numerous demonstrations have taken place in Jordan since January 2011 to call for political and economic reforms and demand an end to corruption. In response, King Abdullah said early elections would be held.
But the Brotherhood says it would boycott the polls as it did in 2010 to protest against the lack of solid reforms, while calling for a parliamentary system where the prime minister is elected, rather than named by the king.
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In an exclusive interview with AFP last month, the king said a decision by the Islamists to boycott the vote was "a tremendous miscalculation."
"As constitutional monarch, my mandate is to be the umbrella for all political groupings and all segments of our society, and as part of that responsibility, I am telling the Muslim Brotherhood that they are making a tremendous miscalculation," he said.
"The countdown to the elections has already started. Registration is under way. We have already crossed the one-million person mark. Parliament will be dissolved. The elections date will be announced. And we will have a new parliament by the new year."
The Islamists and other opposition parties have said they were considering a boycott over a new electoral law under which voters cast two ballots: one for individual candidates in their governorates and one for parties or coalitions nationwide.
King Abdullah has ordered parliament to increase seats reserved for party candidates, urging the Islamists to take part in the polls.
MPs raised the number from 17 to 27, but failed to satisfy opposition groups.
"This elections law is not perfect. We all understand that. But there is no better consensus on an alternative. What is critical is that we keep going forward, and -- mark my words -- we will have a new parliament by the new year," the king said.
"So I am telling the Muslim Brotherhood, you have a choice. To stay in the street or to help build the new democratic Jordan."
According to the constitution, elections take place every four years, but Jordan held early polls in 2010 after the king dissolved parliament.
The Islamists boycotted those elections in protest at constituency boundaries, saying they over-represented loyalist rural areas at the expense of urban areas seen as Islamist strongholds.