MANAMA, Bahrain - A prominent Bahraini opposition leader returned from exile Saturday and urged the kingdom's rulers to back up reform promises with action as thousands of demonstrators marched on government buildings in the capital.

The return of Hassan Mushaima, a senior Shiite figure, could mark a new phase for an anti-government movement in the tiny Persian Gulf nation that is a strategically important American ally. He heads a Shiite group known as Haq, which is considered more hard-line than the main Shiite political bloc that has helped drive two weeks of protests.

He was embraced and kissed by a small group of supporters as he returned Saturday from several months of voluntary exile in London.

Mushaima, who had been among a group of Shiite activists previously accused of plotting to overthrow Bahrain's rulers, called on the government to be more responsive to protesters' demands for far-reaching political reforms.

"Dialogue ... is not enough. Promising is not enough. We have to see something on the ground," he told reporters at the airport. Bahrain's rulers "have promised before but they did not do anything for the nation of Bahrain," he said.

The Bahraini opposition currently appears divided over whether to demand an end to the Sunni monarchy or offer it a chance to remain in exchange for handing powers to the elected parliament.

Mushaima did not call directly for the removal of the monarchy, but insisted any changes should grant more power to the people. Asked if he hoped to lead the protest movement, he said: "I'm always saying to the people, `I'm your servant.'"

His return to Bahrain was briefly delayed when his passport was confiscated during a stopover in Beirut on an Interpol warrant Tuesday. But Bahraini authorities suspended the trial this week, and Lebanon returned his passport Friday.

Daily anti-government protests in Bahrain erupted two weeks ago, as part of a wave of political unrest that is spreading across the Arab world. The movement in Bahrain is led by Shiites who account for about 70 percent of the country's 525,000 people, but have long complained of systematic discrimination and other abuses by the Sunni dynasty that has ruled for more than two centuries.

On Saturday, thousands of protesters marched from the capital's landmark Pearl Square into the Bahraini capital's government and business district.

The roughly 4 kilometre round trip took demonstrators past the prime minister's office, where they called for him to resign. A few police deployed near the government office compound, which also includes the foreign affairs ministry, watched but did nothing to intervene.

The march appeared designed to carry demonstrators' demands out of the somewhat remote Pearl Square and into the heart of official Bahrain, where a branch of Starbucks and shiny office towers housing regional bank headquarters stand testament to the country's prosperity.

Many Shiite protesters complain that too little of the nation's oil wealth trickles down to their neighborhoods and villages, and that they have little chance of securing well-paying government jobs.

Tens of thousands marched along major thoroughfares toward Pearl Square a day earlier to boost pressure for sweeping political concessions in what looked to be the largest mass gathering since protests began.

Local newspapers reported Saturday that the government is planning a cabinet shake up that would result in several ministers being replaced, though no official government announcement has been made.

Bahrain is the first Gulf state to be thrown into turmoil by the Arab world's wave of change. The unrest is highly significant for Washington because Bahrain is home to the U.S. Navy's 5th Fleet, which is the Pentagon's main counterweight against Iran's widening military ambitions.