Updated

Prosecutors announced murder and terrorism charges Monday against four people for a knife attack that killed 29 people at a train station, part of an upsurge in unrest the government blames on Muslim extremists.

The announcement by the national prosecutor's office came during a security crackdown launched after the violence in March in Kunming in China's southwest and attacks in the restive Muslim northwest.

The four defendants, a woman and three men, have names that appear to come from the Uighur ethnic minority in the northwestern region of Xinjiang.

Beijing blames the unrest on Uighur militants with ties to foreign terror groups. Uighur activists say the public is frustrated by an influx of settlers from China's Han ethnic majority and discriminatory policies such as a ban on taking children to mosques.

A spokesman in Germany for the Uighur rights group World Uyghur Congress questioned whether the defendants could get a fair trial.

"The trial will only be a political process with the verdicts predetermined," said the spokesman, Dilxat Raxit. "It is impossible for those involving in major incidents to get fair and transparent legal assistance."

The March 1 attack at the Kunming Railway Station in Yunnan province also injured more than 140 people. Four attackers were killed by security forces at the scene and a fifth was captured.

The survivor, a woman identified as Patiguli Tuoheti, was charged with murder and participating in a terror group, according to a statement by the Supreme People's Procuratorate. Three people who state media said were arrested elsewhere two days before the attack were charged with murder and with leading the terror group.

The statement gave no indication when the trial would be held.

Yunnan provincial Communist Party chief Qing Guangrong said previously the group launched the March 1 attack after they tried unsuccessfully to leave China to take part in jihad, or holy war.