The court sentenced the nine adults to five years in jail each on Sunday and handed down three-year terms to each of the three minors.
Manama has accused the defendants of attacking a police patrol with petrol bombs.
On December 2, a Bahraini court sentenced 16 anti-regime activists to seven years in prison each for allegedly attacking a police vehicle during an anti-government demonstration.
According to Bahrain’s main opposition party, al-Wefaq, the Manama regime's harsh clampdown on pro-democracy activists has intensified over the past months.
In October, Philip Luther, Amnesty International’s director for the Middle East and North Africa, said, “The [Bahraini] authorities simply slap the label 'terrorist' on defendants and then subject them to all manner of violations to end up with a 'confession'.”
Bahrainis have been staging demonstrations since mid-February 2011, calling for political reforms and a constitutional monarchy, a demand that later changed to an outright call for the ouster of the ruling Al Khalifa family following its brutal crackdown on popular protests.
Scores have been killed, many of them under torture while in custody, and thousands more detained since the popular uprising started in the kingdom.
Physicians for Human Rights says doctors and nurses have been detained, tortured, or disappeared because they have "evidence of atrocities committed by the authorities, security forces, and riot police" in the crackdown on anti-government protesters.
Protesters say they will continue to hold anti-regime demonstrations until their demands for the establishment of a democratically-elected government and an end to rights violations are met.
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