Bahrain is under tight security as people vote in parliamentary elections following a mass resignation of Shi'ite lawmakers.

Saturday's poll will fill 18 seats abandoned by the main opposition al-Wefaq party. Its lawmakers quit in February because of the government's bloody crackdown on pro-democracy demonstrators.

The opposition says it will boycott Saturday's vote.

Police and security forces have been deployed heavily in the capital, Manama, particularly Pearl Square, the staging point for anti-government demonstrations in the country.

Clashes between security forces and anti-government protesters have killed about 40 people since February with more than 1,000 others detained. The government has defended the crackdown, saying it is needed to reinstate stability.

Bahrain's political opposition comprises, in large part, the nation's majority Shi'ite Muslims, who say they are treated like second-class citizens by the ruling Sunni minority. They have been calling for more rights and for the introduction of a constitutional monarchy.