MANAMA (Reuters) - Unrest spread across the Middle East and North Africa on Thursday as Bahrain launched a swift military crackdown on anti-government protesters and clashes were reported in Libya and Yemen.
Troops in armored vehicles took control of the Bahraini capital after police firing buckshot and teargas drove out protesters hoping to emulate those who toppled veteran leaders in Egypt and Tunisia.
It was the worst violence in the Saudi-allied Gulf island kingdom in decades and a sign of the nervousness felt by Bahrain's Sunni al-Khalifa royal family, long aware of simmering discontent among the country's majority Shi'ites.
Four people were killed, 231 were injured and opposition leaders said dozens were detained and about 60 were missing.
"They are killing us!" one demonstrator told Reuters.
On the other side of the Arabian peninsula in Yemen, four protesters were killed in the port of Aden in demonstrations that began seven days ago.
In the capital Sanaa, at least 40 people were injured as hundreds of government loyalists, some armed with guns, charged about 1,500 protesters, who threw rocks at them.
Demonstrators want rid of President Ali Abdullah Saleh, who has ruled for 32 years but is seen by Washington as a key ally in its fight against al Qaeda militants based in Yemen.
In Libya, there were reports of five deaths in a rare show of defiance against leader Muammar Gaddafi.
A resident of the eastern city of Benghazi told Reuters there were clashes in the nearby town of Al Bayda between government supporters and relatives of two young men killed during a protest a day earlier.
A Benghazi resident said at least five people had been killed in violence in nearby towns but it was impossible to establish an exact death toll.
A "Day of Rage" in the North African country promoted on social media websites showed little sign of activity in the capital Tripoli, where supporters of Gaddafi, in power for 42 years, held a rally in his support.
In Iraq, two people were killed and 47 were injured when police opened fire on anti-government protesters in the northern city of Sulaimaniya, a police source and witnesses said.
"Profound social and economic issues throughout the Middle East and North Africa will continue to serve as a driving force for further unrest," said political risk analyst Anthony Skinner at the Maplecroft consultancy. "Protests in Bahrain and Libya reflect the ease with which protests have spread in the region."
Such worries helped push Brent crude prices to a 28-month high of $104 a barrel at one point on Thursday and were a factor in gold prices extending early gains to five-week highs.
However, Britain's security minister, Pauline Neville-Jones, said in an interview that revolts by young Arabs seeking freedom were a "huge opportunity" for Western counterterrorism because they weakened al Qaeda's argument that democracy and Islam were incompatible.
It was two months to the day since a young Tunisian, Mohamed Bouazizi, triggered the wave of protests by setting himself alight on December 17 outside a government office in the rundown city of Sidi Bouzid. He was venting frustration at grinding poverty, official corruption and police brutality.
Since Tunisia's autocratic ruler Zine al-Abidine Ben Ali fled a month later, followed a week ago by Hosni Mubarak in Egypt, opposition groups in a dozen or more countries have lived in hope the Arab world might experience a "domino effect" of the kind that swept communists from power in eastern Europe in 1989.
Oil and gas riches, as well as formidable police forces, give rulers the means to fend off challenges. The way in which Ben Ali and Mubarak were overthrown after their armies refused to crush popular uprisings has given many pause.
A Saudi source said on Thursday Ben Ali, who sought refuge in Saudi Arabia, was in a "grave condition" in a Saudi hospital.
Leaders from the Gulf to the Atlantic have announced a variety of measures to ease rising food prices and unemployment and to enhance political participation.
The oil-rich United Arab Emirates said on Thursday it would treble the number of people the rulers would choose to vote for members of an advisory body that serves as a form of parliament.
Middle Eastern leaders have also tightened security.
The army in Bahrain, a country of 1.3 million people out of whom 600,000 are native Bahrainis, issued a warning to people to stay away from the center of the capital and said it would do whatever was needed to maintain security.
At Pearl Square in central Manama, abandoned tents, blankets and rubbish were scattered about and the smell of tear gas wafted through the air.
Helicopters flew over the city, which is a regional hub for banks and home to the U.S. Navy's Fifth Fleet.
The protesters want the Sunni ruling family to relinquish its control over top government posts and address grievances held by the country's majority Shi'ites who complain of economic hardships, lack of political freedom and discrimination in jobs in public service and the military in favor of Sunnis.
The sectarian aspect of the violence in Bahrain could fuel discontent among the Shi'ite minority in neighboring Saudi Arabia, the world's biggest oil exporter.
"This is real terrorism," said Abdul Jalil Khalil of Bahrain's Shi'ite party Wefaq, which said it would withdraw from a parliament, which has limited powers. "Whoever took the decision to attack the protest was aiming to kill."
Western powers have been caught in a dilemma between backing rulers whom they see as bulwarks against anti-Western Islamists and at the same time being seen to promote democracy.
In Bahrain, Saudi and Western officials fear majority rule could help their adversaries in Shi'ite-ruled Iran.
U.S. Secretary of State Hillary Clinton said Washington supported "real, meaningful" change in Bahrain, which she called "a friend and ally," and called on the government to show restraint.
Writing by Alastair Macdonald and Philippa Fletcher; editing by Andrew Dobbie and Eric Beech