Thousands rallied on Friday in an officially authorised protest called by the main opposition group al-Wefaq. But as the event ended around 100 demonstrators clashed with police, the group said on Saturday, which left a second young protestor dead in six weeks.
Witnesses on Friday said riot police used tear gas and stun grenades to disperse those demonstrators, who, the authorities said, were throwing petrol bombs and wielding iron bars.
The police described the incident after the protest as a "terrorist attack" on a security patrol that "targeted the lives of members of the patrol" late on Friday evening.
The police had defended themselves "according to their legal authority", a statement said, confirming one of the protesters had died.
Bahrain, headquarters of the US navy's fifth fleet, has been in turmoil since mass demonstrations started at the height of Arab Spring unrest last year, led by its Shi'ite Muslim minority.
The protests were put down by the Sunni monarchy which imposed martial law and invited Saudi Arabia to send troops in support.
In mid-August a 16-year-old protester was killed in a similar incident, when police opened fire with birdshot during clashes after a demonstration, opposition activists said.
The opposition says more than 45 people have been killed in protests since martial law was lifted in June 2011. The interior ministry says protesters have injured more than 700 police officers and that the authorities have exercised restraint.
Al-Wefaq named the dead protester as 17-year-old Ali Hussain Nima and distributed photographs show a body covered in blood and flecked with birdshot wounds. The pictures could not be independently verified.
Bahrain and Saudi Arabia accuse Iran of fomenting the unrest in the island kingdom and among Saudi Arabia's Shi'ite Muslim minority, who mostly live in a province situated next to Bahrain. Iran denies the accusations.
The death comes a day after the UN Human Rights Council appointed a Bahraini as the Asia representative to its advisory committee. – Reuters