BEIJING, Jan 8 (AFP) - Amnesty International Wednesday denounced a spate of heavy sentences recently imposed on Chinese dissidents, saying the trials showed Beijing's "determination to crush any form of dissent."

"They also show the authorities' readiness to misuse the law for their own political purposes and to pass heavy sentences on innocent victims as a warning to others," the human rights watchdog said in a letter to Chinese Premier Li Peng.

Amnesty highlighted the cases of Tibetan musicologist Ngawang Choephel, whose sentencing to 18 years in prison for spying was announced by radio on December 26, and activist Li Hai, who was imprisoned for nine years on December 18 for "revealing state secrets."

"Ngawang Choephel and Li Hai are prisoners of conscience who should be immediately and unconditionally released," the letter said. "The nature of their cases and harshness of the sentences run counter to Chinese government claims of improvements in human rights."

Amnesty also cited the December 6 sentencing of two ethnic Mongol intellectuals for "separatist activities."

Hada and Tegexi (eds: one name each), who received 15- and 10-year sentences respectively, were carrying out peaceful political activities and should be considered prisoners of conscience, the group said.