Chinese officials say that members of the country's Muslim Uighur ethnic minority have gone overseas to fight with ISIS, which controls sections of Syria and Iraq, and returned to take part in plots at home.

Authorities in the far-western region of Xinjiang, which borders Afghanistan and Pakistan, will strengthen their crackdown on terrorism and extremism, regional representatives said at a discussion on the sidelines of China's legislature.

Xinjiang has seen repeated violence as Uighurs have bristled under what they say is repressive Chinese government rule. Attacks blamed on Uighurs have also occurred in other parts of the country, including a car which plowed into Beijing's Tiananmen Gate in 2013, killing five people.

"There are Uighurs that have fled overseas and joined the Islamic State," Zhang Chunxian, Communist Party secretary of Xinjiang, said Tuesday. "The organization has a huge international influence and Xinjiang can't keep aloof from it and we have already been affected. We have also found that some who fought returned to Xinjiang to participate in terrorist plots." He didn't elaborate.

Beijing has previously blamed the violence on Islamic militants with foreign connections who are seeking an independent state in Xinjiang, but has offered little evidence and ignored calls for independent investigations. Uighur groups say police have used indiscriminate deadly force against people protesting the government's policies in the region.

The Global Times, a newspaper affiliated with the ruling Communist Party, said in December that about 300 Chinese are fighting alongside ISIS in Iraq and Syria.

Raffaello Pantucci, a London-based terrorism researcher at the defense think tank Royal United Services Institute, said it was possible that people from Xinjiang had fought in Syria and Iraq and with ISIS. "Whether individuals are able to make the journey all the way back seems difficult, especially given the difficulty people from Xinjiang seem to have in getting passports," he added.

Pantucci said it was not clear whether ISIS was letting foreign fighters leave. "We have seen numerous reports of foreigner fighters getting executed for trying to leave, including groups of Uighurs," he said.