Five suicide bombers carried out the attack which killed 31 people in the capital of China’s troubled Xinjiang region, state media reported a day after the deadliest terrorist attack to date in the region.

The incident, which occurred in Urumqi on Thursday morning, was the second suicide attack in the capital in just over three weeks. A bomb and knife attack at an Urumqi train station in late April killed one bystander and wounded 79.

The government recently launched a campaign to strike hard against terrorism in Xinjiang, blaming Islamists and separatists for the worsening violence in the resource-rich western region bordering central Asia. At least 180 people have been killed in attacks across China over the past year.

The attackers ploughed two vehicles into an open market in Urumqi and hurled explosives. Many of the 94 people wounded were elderly shoppers, according to witnesses.

“Five suspects who participated in the violent terrorist attack blew themselves up,” the Global Times, a tabloid run by the People’s Daily, the official newspaper of the Chinese Communist Party, reported on Friday.

The newspaper said authorities “are investigating whether there were other accomplices”.

“Judging from the many terrorist attacks that have taken place and the relevant perpetrators, they have received support from terrorist groups outside China’s borders as well as religious extremist propaganda spread via the internet,” Chinese Foreign Ministry spokesman Hong Lei said at a daily news briefing.

No group has claimed responsibility for Thursday’s attack.

Pan Zhiping, a retired expert on Central Asia at Xinjiang’s Academy of Social Science, said Thursday’s attack was the deadliest ever in the region.

He said the “terrorists” received training overseas from groups like the East Turkestan Islamic Movement (ETIM) and gained combat experience in Syria.

“They are now definitely organized and these small organizations are very tight,” Pan said. “If it’s not possible to crack a small organization, then I think this kind of thing will continue to happen.”

SPREADING “TERRORISM PROBLEM”

Exiles and many rights groups say the real cause of the unrest in Xinjiang is China’s heavy-handed policies, including curbs on Islam and the culture and language of ethnic Uighurs, Turkic speaking Muslim people.

The Uighurs have long complained of official discrimination in favor of the Han people, China’s majority ethnic group.

Residents said the morning market, where the attack occurred, was predominantly frequented by Han Chinese customers, though many of the vendors were Uighurs.

A Han Chinese man, surnamed Zheng, said he had left the market just 20 minutes before the attack occurred. He said after he heard the blast, he rushed back to see plumes of black smoke rising into the sky and people running away.

“How are people supposed to live life when you can’t even go to buy vegetables? It’s so terrible,” he told Reuters.

“I just got here, but if I had the means, I’d consider leaving Urumqi for someplace safer,” Zheng said, adding that other morning markets were also closed.

China has been grappling with a rise in suicide attacks. A car burst into flames at the edge of Beijing’s Tiananmen Square in October, killing five people.

Chinese police blamed the ETIM for the Urumqi train station attack last month, state news agency Xinhua said on Sunday, the first time the separatists have been directly linked to the assault.

The ETIM has been accused by the United States and China of having ties to al Qaeda, but there is disagreement among security experts over the nature of the group and whether ties with al Qaeda and other militant organizations really exist.

“It looks like (the Chinese authorities) have a metastasizing domestic terrorism problem,” Kenneth Lieberthal, a China expert with the Brookings Institution, told Reuters.

“I think the evidence suggests to date that if anything, the rethink (on Xinjiang policy) will be to get tougher.”