China's official Xinhua news agency said late on Thursday that to date China has convicted 42 people for their role in the riots while another 116 await trial. Some 953 people were detained by the police, Xinhua said, quoting Palma Trily, the No. 1 vice-chairman of the Tibet Autonomous Region government.
He did not give details on the length of the latest 12 sentences handed down on June 19 and 20 but said neither these rioters nor 30 people convicted earlier had received death sentences.
Those jailed or on trial have been charged for their roles in riots in Tibet's capital, Lhasa, on March 14, Xinhua reported. Their crimes include arson, robbery and assaulting government offices, according to Xinhua.
Peaceful protests that began on March 10 in Lhasa to mark the anniversary of a 1959 uprising against China's rule of Tibet escalated into widespread violence across the city on March 14.
China says 18 "innocent civilians" and one policeman were killed in the riots.
However, Tibet's government-in-exile says more than 200 people were killed in the Chinese crackdown on the unrest, which spread to other parts of western China that have Tibetan populations.
Some information for this report was provided by AFP and Reuters