Security forces confirmed they had fired warning shots at the crowds and one young man had been killed in the protests, which began in the early morning and lasted almost all day.

The interior ministry said a security official was killed in a ” terrorist attack” using what it said was an inflammable projectile, according to a statement on its Twitter account.

The clashes were the most violent in recent months and could mar talks that began on Sunday between mostly Shi’ite Muslim opposition groups and the Sunni-dominated government to try to end political deadlock in Bahrain, which is home to the US Fifth Fleet.

Bahrain has seen almost daily demonstrations in the run-up to the anniversary of the revolt, which has put the kingdom on the front line of a region-wide tussle for influence between Shi’ite Muslim Iran and Sunni Arab states such as Saudi Arabia.

Mass protests that erupted in February 2011 at the height of the Arab Spring were crushed, but small demonstrations demanding greater rights for Bahrain’s Shi’ite majority and an end to the absolute power of the Sunni ruling family have continued.

Bahrain’s chief of public security, Brigadier-General Tariq Al Hassan, said police had fired warning shots on Thursday to disperse a crowd that had attacked them with fire bombs, stones and iron rods, injuring several, some seriously.

“Officers discharged birdshot to defend themselves. At least one rioter was injured in the process. A short time later, a young man was pronounced dead at Salmaniya Medical Center,” he said in a statement.

He said several members of the force involved in the incident were being investigated to determine the circumstances of the death.

The main opposition group Wefaq named the youth was Ali Ahmed Ibrahim al-Jazeeri, a 16-year-old Shi’ite, and said he had been killed in the village of Diya, near Manama.

It said dozens of others had been hurt, some seriously, and posted pictures of casualties, including a photograph of the dead youth with bandages on his abdomen.