King Abdullah II, a key U.S. ally in the Arab world, has gone through three prime ministers in 18 months as he struggles to avoid the kind of Arab Spring political upheaval that toppled four presidents in 2011.

But despite his most adroit efforts, the Hashemite throne remains vulnerable because, unlike his fellow monarchs in Saudi Arabia and the Persian Gulf states, he doesn't have the money to buy off protesters while pressure for sweeping reform and an end to entrenched corruption is growing.

"The king has shuffled Cabinets and then shuffled them again, using prime ministers as buffers to absorb popular discontent," observed the International Crisis Group, a Brussels think tank.

"He has charged committees to explore possible reforms but these remain largely unimplemented."

On Thursday, Prime Minister Awn Khasawneh resigned only six months after Abdullah appointed him to replace Marouf al-Bakhit, a former army general and head of Jordan's intelligence service, a key pillar of the monarchy.

Bakhit, who was widely perceived as dragging his feet on reform, was forced to step down because he was allegedly involved in a secret deal to build a giant casino complex at a Dead Sea resort.

He had been accused of high-level corruption during a previous spell as prime minister in 2005-07.

Labib Kamhawi, a Jordanian political analyst, said the resignation of Khasawneh, a deputy chief at the International Court of Justice in The Hague and a former adviser to Abdullah's late father, King Hussein, will likely increase pressure on the monarch to introduce reforms.

"There will be increased tension between the palace and popular movements seeking reform," Kamhawi said.

The appointment of Khasawneh, a prominent legal expert widely perceived as a clean politician, as prime minister in October 2011 had been widely seen as a move by Abdullah to accelerate bringing in reforms.

Khasawneh's no-warning resignation came amid rising popular discontent with the glacial pace of reform, with allegations Abdullah was dragging his feet. The palace acknowledged Khasawneh's resignation without comment or explanation and appointed another former prime minister, Fayez al-Tarawneh, who served in the late 1990s.

But few political insiders expect him to be any more successful than his three recent predecessors in producing a formula that will find acceptance by the royal palace and the mainly Islamist opposition.

Abdullah, who ascended the throne after his father died in February 1999, inherited a long-fraught political crisis.

This is essentially a confrontation between the Bedouin tribes who're the traditional bedrock of support for the monarchy established by Britain after World War I and the Muslim Brotherhood, a largely urban movement linked to Palestinians who make up some 60 percent of Jordan's population of 6.5 million.

The Bedouin, known as "East Bankers" to distinguish them from Palestinians from the Israeli-occupied West Bank, resent the growing political power of the Muslim Brotherhood's political arm, the Islamic Action Front.

The IAF resents the monarchy's constant efforts to hold them in check, particularly since the pro-democracy uprisings of the Arab Spring that began in January 2011.

"The East Bankers' resentment toward the regime has been building since shortly after King Abdullah II's ascension to the throne … and his move toward liberalization," observed the U.S. global security consultancy Stratfor.

The largely rural East Bankers, around 40 percent of Jordan's population, have long dominated Jordan's public sector, the army, security forces and the bureaucracy. They still dominate Parliament despite Islamist gains, which have been repeatedly thwarted to prevent them gaining a majority.

But, Stratfor notes, "this has not offset the East Bankers' concerns about a loss of position due to what they see as the Palestinian majority increasingly gaining privileges at their expense."

The big fear is, of course, that Jordan will eventually become a Palestinian state.

On April 17, nine days before Khasawneh resigned, the lower house of Jordan's parliament approved a measure to the draft political parties law that forbids the establishment of parties based on religion.

That was designed to disqualify the IAF from upcoming elections, thus antagonizing the Islamists at a time when the king insists he's striving to introduce reforms.

With Abdullah trying to rebuff mounting Saudi pressure to use Jordan as a conduit for arms and fighters to escalate the 13-month-old uprising against the Iranian-backed regime in Damascus, Jordan looks set for a rough ride in the months ahead.