Anti-government protesters have occupied a central square in Bahrain's capital, Manama, demanding political reform and a more direct say in government.
At least six have been killed and hundreds wounded in clashes with riot police this week, prompting the king to appoint the crown prince to talk to protesters.
Although Shi'ite Muslims make up 70 percent of the local population, they say the ruling Sunni minority shuts them out of state jobs, housing and healthcare.
The government denies this, and the introduction of a new constitution and parliamentary elections a decade ago had helped calm Shi'ite discontent.
But tensions flared again ahead of elections in October 2010, when the government was accused of changing voting districts in order to maintain its majority against the Shi'ite opposition in Bahrain's 40-seat parliament.
Following are some facts about political groups in Bahrain.
The final say on politics in Bahrain rests with the ruling al-Khalifa family, from which at least half of the cabinet's ministers and many government officials hail.
Bahrain is led by King Hamad bin Isa al-Khalifa, who wields ultimate authority, although Prime Minister Sheikh Khalifa bin Salman al-Khalifa has governed the country since independence in 1971.
Analysts and diplomats regard Sheikh Khalifa as reluctant to agree to reforms and as mostly concerned with maintaining the ruling family's control of politics and the economy.
Crown Prince Sheikh Salman bin Hamad al-Khalifa, however, is credited with being more open to reforms, in particular economic modernization. He is viewed as more conscious of the need to provide jobs for the small island kingdom's young population.
Sheikh Salman chairs the Economic Development Board, which has the last word on all matters related to economic policies.
Al Wefaq is the largest Shi'ite opposition bloc. It boycotted the 2002 election but took part in 2006 and 2010.
In the latest election, it gained one seat for a total of 18, but said on Thursday it was pulling out of the assembly after security forces stormed a demonstration in the central square, killing four people.
Al Wefaq has sometimes cooperated with Sunni blocs to question the government over the finances and management of state-owned companies, as well as opposing state subsidies cuts.
But it has also accused the government of failing to push through political reforms.
The mainly Shi'ite Haq movement for Liberty and Democracy disputes the legitimacy of the political reform process launched by the king a decade ago.
Haq's popularity was underscored when weeks of protests followed the arrest of its leader Hassan Mushaima in January 2009 on charges of plotting to overthrow the government.
Mushaima was pardoned by the king in April of the same year.
AL ASALAH AND AL MENBAR
The Sunni Al Asalah Islamic Society is part of a wider movement of Islamists who have been vocal in demanding a ban on alcohol sales in Bahrain.
In 2006, Al Asalah coordinated its candidates with fellow Sunni Islamist group Al Menbar National Islamic Society to stand a better chance of winning seats against Al Wefaq.
Al Menbar is the political wing of the Al Islah Society, associated with the Muslim Brotherhood.
The leftist National Democratic Action Society, or Waad, is a secular group, but has not yet managed to win a parliamentary seat.
(Reporting by Frederik Richter; editing by Mark Heinrich)