(Updates with arrest of five in relation to Maqsha bomb)
MANAMA, April 27 (Reuters) - Bahrain's Supreme Criminal Court has sentenced eight people to life in prison for their part in the killing of a policeman in a bomb blast in November, the prosecutor's office said on Sunday.
The Sunni-ruled Gulf Arab kingdom and host of the U.S. Fifth Fleet has struggled with unrest since mass pro-democracy protests, led by the majority Shi'ite population but also included some Sunnis, erupted in 2011.
The protests were put down by the authorities but since then more radical Shi'ites have carried out low-level violence against security forces on an almost daily basis. Recent months have seen a rise in the use of homemade bombs.
The prosecutor's office said the eight men planted a homemade bomb close to where police usually erected a checkpoint during protests, before setting tyres on fire and blocking the road to lure police to the site.
One policeman was killed and four others were injured in the resulting blast, the prosecutor said.
Bahrain's main opposition group, al-Wefaq, said on its website that detainees were regularly subjected to torture and forced to make confessions and that the courts were ignoring human rights violations committed by the security forces.
The Bahrain government says it has taken steps to address security forces' violations by dismissing those responsible and introducing cameras at police stations to monitor abuses. But activists say this has not helped.
Shi'ites in the kingdom have long complained that they are underrepresented in elections and that they face discrimination in getting government jobs. The government denies discrimination.
Also on Sunday, the Interior Ministry said it had arrested five people in relation to another explosion that took place in the Shi'ite village of Maqsha on April 19.
Two people were killed in a car when a homemade bomb they were transporting in order to blow up a police checkpoint exploded, and another was injured.
The ministry is still looking for two more suspects in relation to the explosion, the ministry said on its website. (Reporting by Farishta Saeed; Writing by Angus McDowall and Maha El Dahan; Editing by Alison Williams)