Fifteen Falun Gong sympathizers were sentenced Friday to up to 20 years in prison for hacking into a cable television system to show protest videos in two Chinese cities, a court official said. 

The incident on March 5 marked the start of a campaign by Falun Gong supporters who have commandeered TV signal in at least four areas to show videos opposing China's 3-year-old crackdown on the banned spiritual movement. 

The defendants were convicted Friday in the northeastern city of Changchun of violating anti-cult laws and damaging broadcast equipment, said the official of the Changchun Intermediate-Level People's Court. He would give only his family name, Cao. 

The defendants received sentences ranging from four to 20 years in prison, Cao said. He said several defendants had filed appeals. 

China banned Falun Gong in 1999 as a threat to public order and communist rule. Thousands of people have been detained in an often brutal crackdown. 

Falun Gong activists abroad say hundreds of supporters have been killed in detention. Chinese officials deny killing detainees but say some have died in hunger strikes or from refusing medical help. 

The March 5 broadcasts in Changchun and nearby Songyuan criticized the 1999 ban, according to residents who saw them. They said it showed scenes of Falun Gong founder Li Hongzhi, a former Chinese government employee who lives in the United States. 

The longest sentences imposed Friday went to two defendants identified by Cao as Zhou Runjun and Liu Weimin. 

"They are chief criminals who were both organizers and main destroyers in the case," Cao said. He wouldn't elaborate. 

However, a Changchun police spokesman earlier said Liu and another defendant were engineers who had experience with electrical equipment. 

Most of the other defendants were unemployed, according to the spokesman, Li Shichang. A senior official in June referred to Falun Gong sympathizers who have hijacked broadcasts as "skilled and professional." 

The television break-ins have embarrassed the government, which denounces the broadcasts as "reactionary propaganda" and says they threaten social order. 

In June, a state-run satellite system briefly displayed messages of support for Falun Gong in a TV broadcast after its signal was hijacked. The government has responded with measures aimed at tightening control of television and satellite systems. 

Falun Gong sympathizers also have used e-mail and the World Wide Web to spread protest messages, as well as clandestinely posting flyers in Chinese cities.