A court in Myanmar has imposed new sentences with hard labor for six prominent activists who are already serving prison terms for their political activities.

All six activists faced charges including disrupting public tranquility, deterring a public officer from carrying out his duty and for rioting and violating a peaceful assembly law for protesting outside China's Embassy last year.

They were protesting the shooting death last year of an opponent of a Chinese-backed copper mine.

All 6 were sentenced Friday to 4 years and 4 months imprisonment with hard labor. Their previous sentences were for violating the peaceful assembly law with their political activities.

An independent political prisoner association has tallied 158 prisoners of conscience and 450 others facing trial in Myanmar for their political activities as of May.