BEIRUT (Reuters) - A Bahraini police crackdown on pro-democracy protesters, two days after Saudi Arabia sent in 1,000 troops to bolster its longtime Gulf Arab ally, will heighten Sunni-Shi'ite tensions in Bahrain and beyond.
At least five people were killed and hundreds wounded when police cleared demonstrators from Manama's Pearl Square on Wednesday in an attempt to halt weeks of popular unrest.
The violence, so soon after the Saudi-led intervention, will further embarrass Washington, which had urged dialogue to tackle Bahrain's problems and says Riyadh did not consult it before moving troops to the island where the U.S. Fifth Fleet is based.
That may be the case, but U.S. Defence Secretary Robert Gates visited Bahrain at the weekend. To many Arabs the timing smacks of U.S. complicity in King Hamad bin Isa al-Khalifa's decision to invite the Saudis in and declare martial law.
"That will create a narrative that does not make the U.S. look good," said Shadi Hamid of the Doha Brookings Centre.
"It puts the U.S. on one side of the conflict, which is with the status quo and the Bahraini ruling family."
Non-Arab Iran, which has in the past laid claim to Bahrain, has denounced what it sees as U.S.-backed Gulf Arab meddling.
"It is not possible to stop a popular uprising by using armed forces of other countries," said Iranian President Mahmoud Ahmadinejad. "These are ugly and failing actions."
The United Arab Emirates, Qatar and Oman say they are also sending contingents or personnel to Bahrain as part of a joint defence force of the six-nation Gulf Cooperation Council (GCC).
The decision to crush a protest movement inspired by popular revolts in Egypt and Tunisia is conditioned by the sectarian factor in Bahrain, a tiny country seen by the United States and the GCC as a bulwark against the rising power of Shi'ite Iran.
Sunni Gulf rulers tend to view Shi'ites in Bahrain and Saudi Arabia as a potential fifth column for the Islamic Republic, despite what Gulf-based political analyst Neil Partrick called the "clear Arab affinity of many of the Shi'ites of the Gulf."
The clampdown in Bahrain suggests that a conservative wing of the ruling family, backed by its Saudi counterparts, has won out over reformers led by Crown Prince Sheikh Salman bin Hamad al-Khalifa, who last month offered dialogue with the Shi'ite opposition and said protesters could stay in Pearl Square.
A main demand of Bahrain's pro-democracy movement has been the resignation of conservative Prime Minister Sheikh Khalifa bin Salman al-Khalifa, who has held his post for 40 years.
Bahraini Shi'ites have long complained of discrimination in housing and jobs, charges the government rejects. The protesters had sought to cast their movement as national, not sectarian.
Hamid said the mainstream Shi'ite opposition parties in Bahrain had no ties to Iran, which had few means to counter the Saudi military intervention directly. "Some of the hardline groups may have ties with counterparts in Iran, but again, that doesn't really tell us much about what Iran can do."
But amid the tumult of Middle East protests, the sectarian overtones of the Bahrain crisis find a ready echo in places like Iraq and Lebanon, where Sunni-Shi'ite tensions run high.
Iraqi radical Shi'ite cleric Moqtada al-Sadr has called for rallies in support of the Bahraini protesters. Lebanon's pro-Iranian Shi'ite Hezbollah movement has done likewise.
They point to Bahrain as evidence of U.S. double standards in dealing with uprisings in the Gulf and north Africa.
Partrick said any such difference "reflects the fact that the Gulf Arab family-based regimes do not have the option of the Egyptian or Tunisian regime of obliging an unpopular leader to take a long vacation without the whole edifice being at risk."
Gulf autocrats clearly have no interest in seeing Bahrain's rulers bow to popular demands for a constitutional monarchy.
That risks energising similar challenges to their own power and privilege, which they have hitherto smothered by using a portion of their oil wealth to buy political quiescence.
"The United States has to back the status quo in the Gulf as the local leaders are an important part of a U.S.-led prop against Iran," Partrick said.
"Washington will cajole in favour of more accountability and more empowered legislatures where it can, but will not wish to fundamentally weaken these allies as it did the Shah of Iran."
The United States has urged all sides in Bahrain to show restraint, but has not criticised the Saudi intervention.
Hamid, of Brookings Doha, said Washington did not want full democracy in Bahrain and was not on the side of the protesters.
"Bahrain is a red line for the U.S., perhaps in a way that Egypt wasn't," he said. The Fifth Fleet base was vital to U.S. projection of power in the region and in countering Iran.
"That is generally America's problem throughout the Arab world right now. Its interests are clashing with its ideals and its interests seem to be winning out," Hamid added.
Arabs had sensed that U.S. President Barack Obama had eventually done the right thing in Egypt by pressing Hosni Mubarak to quit. But since then there had been a return to backing dictators and believing their reform promises were sincere, he said, citing U.S. policy towards Yemen and Bahrain.
Hamid said the United States risked putting itself on the wrong side of history. "If Arabs perceive the U.S. standing against their aspirations, that will further damage American influence and credibility in the coming years and decades."
Editing by Mark Trevelyan