BEIJING -- Authorities in southwestern China on Tuesday executed three men convicted of masterminding a knife attack a year ago that killed 31 people outside a railway station in the city of Kunming.

Iskandar Ehet, Turgun Tohtunyaz and Hasayn Muhammad were put to death after China's Supreme Court upheld their convictions for the crimes of murder and organizing and leading a terrorist organization, the Kunming City Intermediate People's Court said in a notice.

Five knife-wielding assailants hacked 31 people to death and injured 141 on March 1, 2014, an act of violence that shook the country as tensions between the Uighur Muslim minority and the majority Han ethnic group spread beyond the Uighurs' homeland of Xinjiang.

Four of the assailants were shot dead at the scene and the fifth, a pregnant woman, Patigul Tohti, was captured alive and later sentenced to life in prison on the charges of joining a terror group and murder.

Authorities said Ehet, Tohtunyaz and Muhammad were arrested two days before the attack while attempting to flee across the Chinese border. Having lost contact with the three men, the other five members of the group mounted the attack as planned, the Kunming court said.

Beijing has blamed Uighur separatists and religious fanatics for a spate of recent violence that has caused hundreds of deaths over the past year.

Critics say heavy-handed Chinese rule and economic disenfranchisement have pushed some Uighurs toward extremism.

Dilxat Raxit, spokesman for the Germany-based World Uyghur Congress, said he did not believe the defendants had a fair trial. "China is evading the root cause for the problem through the political means of the death sentence," Dilxat Raxit said. "The defendants were not granted a dignified trial."