BEIJING (AP) -- Eighteen people who took part in violence that killed almost 100 people near China's border with Pakistan last month have handed themselves in to authorities, Chinese state media said Sunday.

Authorities say a terrorist gang attacked a police station and government buildings in Shache county near Kashgar on July 28, killing 37 people before police shot dead 59 of the attackers.

Xinjiang has experienced rising unrest in recent months blamed on militants from the region's native Muslim Turkic Uighur ethnic group who are seeking to overthrow Chinese rule. Of the 37 civilians who were killed, 35 were Han Chinese and two were Uighur, according to the official Xinhua News Agency. It has not released any details about the attackers. 

The Xinjiang Daily, the region's official newspaper, reported Sunday that 18 people had since surrendered because of a publicity campaign urging local people to provide tip-offs about who was involved in the violence. It said that most of the 18 were ``ordinary people,'' some of whom had been instigated or coerced into taking part in the violence without knowing the reasons for it, and that because they had surrendered would be dealt with ``leniently.'' 

But a spokesman for a Munich-based Uighur rights advocacy group said the 18 had surrendered out of fear for their lives. Amid a manhunt for the participants in the violence, armed forces encircled a corn field where the 18 Uighur farmers, the youngest of whom was 15, had retreated and were shooting in the air, said Dilxat Raxit of the World Uyghur Congress.

He said authorities took their family members and other relatives to the field and gave them loudspeakers to persuade them to give up, ``telling them the government can ensure their safety after they surrender.''

Neither account could be independently verified.  

The Shache incident appeared to be the most serious single instance of bloodshed in Xinjiang since riots broke out in 2009 that left nearly 200 people dead. The World Uyghur Congress has disputed the official version, saying that police killed Uighurs who had been protesting the authorities' heavy-handed security crackdown during the Muslim holy month of Ramadan.

Last week, the regional government announced it had arrested 215 people in relation to the attack.

People who answered the phones at the Shache county government and police offices said they had no information.