"We have heard that 30 people, Uighurs, were executed by a firing squad," Yusupbek Mukhlisi, leader of the United National Revolutionary Front of East Turkestan, said in the capital Almaty.
He said that the public executions were carried out in the town of Yining, about 50 kilometres (30 miles) from the Kazakh border in China's north- western Xinjiang province, last Friday.
"When the parents and families saw this, they lost their patience," said Mr Mukhlisi. He said that the executions fell on the fifth anniversary of the decision made by some Uighur separatist groups to use violence to secure independence from Peking.
Chinese sources say 10 people were killed and about 100 wounded in the resulting riots by pro-separatist Uighurs. However, Mr Mukhlisi said the casualties were higher, with 25 Uighurs and 55 Chinese soldiers killed in the violence.
Chinese residents in Yining, called Kuldzha by the Uighurs, said the town had been sealed off by Chinese police and that a curfew was in place following the riots. Mr Mukhlisi said hundreds of Uighurs had been arrested after the rioting. "They have run out of room at the prisons and are putting people in cellars," he said.
Information from the remote region is difficult to verify. Mr Mukhlisi said telephone lines to and from Kazakhstan had been cut, and most information was reaching Almaty from Uighur travellers.
A Chinese official source in Almaty said the unrest was to be expected. "It is a multi-ethnic region so it doesn't surprise me," said the source.
The region is home to ethnic Kazakhs and Kyrgyz as well as Uighurs and Han Chinese. "The [Uighur] separatists are stirring this up," the source added.
Local authorities have played down the extent of the rioting, describing it as a small incident started by "foreign hostile forces".
The Xinjiang authorities last year cracked down on the Uighur separatists, Turkic-speaking Muslims who make up the majority of the region's population, after a series of violent clashes, bombings and assassination attempts on officials and Muslim leaders regarded as pro-Peking.
Peking also imposed tougher border controls along the vast region of mountains and desert, saying it wanted to halt the smuggling of arms from the neighbouring central Asian states of Kazakhstan, Kyrgyzstan and Tajikistan.