China is tightening border controls in its northwestern Xinjiang region amid rising terrorism threats, the regional governor was quoted as saying on Tuesday.

State media reported Shohrat Zakir made the pledge in a speech at the region's main annual political meeting on Monday, saying increased measures taken in the last year would be further strengthened.

The crackdown seeks to prevent suspected insurgents both from leaving Xinjiang to fight abroad and from returning to the region after receiving military training overseas, the official China Daily newspaper said.

Xinjiang has long been home to a simmering insurgency against Beijing's rule waged by extremists among the native Turkic-speaking Uighur ethnic group, who are mainly Muslim and culturally distinct from most Chinese. Many Uighurs already face onerous restrictions on where they can work and travel to, including extreme difficulties in obtaining passports.

Xinjiang shares a border with Afghanistan, Pakistan and four nations in the often volatile Central Asian region, whose native populations share ethnic, linguistic and religious links with Uighurs. Uighur extremists have also been reported to have joined the fighting in Syria and were blamed for a deadly attack on a Buddhist temple in Thailand.

Xinjiang has been smothered in heavy security since deadly riots in 2009 that pitted Uighurs against ethnic Han Chinese migrants in the regional capital of Urumqi. Those measures were tightened further following a wave of attacks blamed on Uighur separatists striking in Xinjiang and other parts of China, including the capital Beijing.

While such incidents have largely been curtailed, three knife-wielding assailants last month attacked staff at a Communist Party office in southern Xinjiang's Hotan region and set off an explosive device, killing two and injuring three others. The attackers were then shot dead by police.

The incident was the first publicly reported fatal attack in months in Xinjiang, where information is strictly controlled and reporting access highly limited.

Prior to that, police in November 2015 killed 28 people who authorities said had killed 11 civilians and five police officers at a remote Xinjiang coal mine controlled by members of China's main Han ethnic group.

Additionally, a Chinese state media outlet reported that three alleged assailants wanted in relation with a 2015 terrorist incident in Hotan were killed in a police raid on Sunday. No details were given.

Beijing's critics say the violence in Xinjiang is prompted by government policies that have marginalised Uighurs in their native region, which has seen a massive influx of Han Chinese who dominate the local economy, security forces and civil service. Some Uighurs are also believed to have been radicalised by extremist ideologies that have spread from Central Asia to the Middle East.