* Policemen attacked while on patrol outside Manama
* Unrest continues to rattle Gulf Arab kingdom
ABU DHABI, Oct 19 (Reuters) - A policeman in Bahrain was killed and another critically injured in a bomb attack while on patrol south of the capital Manama, security officials said on Friday, as further unrest convulsed the Gulf Arab kingdom and close U.S. ally.
Bahrain, where the U.S. Fifth Fleet is based as a bulwark against Iran, has been volatile since majority Shi'ite Muslims began protesting against alleged discrimination last year.
Those protests were initially crushed by the kingdom's Sunni Muslim monarchy, with martial law and help from Gulf neighbours. However, smaller scale demonstrations have since resumed and anti-government protesters clash with security forces several times every week in the small island country.
The policemen were attacked in the village of Akr late on Thursday by rioters with petrol bombs and an unspecified "explosive device", the information authority said in a statement, citing Major General Tariq Hasan al-Hasan, the security chief.
One policeman died of his injuries on Friday morning while the other was in a critical condition, it said. An investigation was underway to find the assailants, Hasan said.
Earlier on Friday, Bahrain's interior ministry described the incident in the mostly Shi'ite village as a "terrorist attack".
Thousands of people attended the policeman's funeral in the mainly Sunni area of Rifaa on Friday afternoon, witnesses told Reuters.
Some mourners shouted "Down, down with Issa Qassim", in reference to Sheikh Issa Qassim, a spiritual guide to Shi'ites in Bahrain. Qassim is not connected to any party but led a pro-democracy protest of some 100,000 people in March.
Bahraini police have been the target of such bombings several times in the past year, most recently in May when four policemen were wounded.
Shi'ites complain of discrimination in the electoral system, jobs, housing and education and say they are mistreated by government departments, the police and the army. Government promises of action to address their concerns have come to nothing, they say.
An anti-government demonstration attended by thousands and organised by the main al Wefaq opposition bloc on Friday afternoon west of Manama passed off peacefully, witnesses said.
A commission of international legal experts reported in November that torture had been systematically used on protesters to punish them and extract hundreds of confessions. It recommended reviewing activists' jail sentences.
Bahraini authorities accuse regional Shi'ite power Iran of encouraging the unrest and have promised a tough response to violent protests as talks with the opposition have stalled.