China executed 13 people Monday for "terrorist attacks" in the violence-wracked northwestern region of Xinjiang, state media said, as death sentences were issued over a suicide car crash at Beijing's Tiananmen Square.

The announcement by the official Xinhua news agency said the 13 were involved in seven different cases connected to Xinjiang, where Beijing says separatist militants are behind a string of attacks that have rocked China in recent months.

Xinhua provided names of four of the executed without identifying them by their ethnicity, though some of the names appeared to be Uighur, a Turkic-speaking mainly Muslim group with cultural and linguistic links to Central Asia.

The report identified two of the cases as taking place last year and resulting in more than two dozen deaths, including those of 24 police officers and ordinary citizens in Xinjiang's Turpan Prefecture in June.

"The execution of criminals involved in terrorist attacks and violent crimes answers the calls of all ethnic groups, deters criminal activities, and demonstrates the resolve of the Communist Party of China and the government in cracking down on terrorism," Xinhua quoted a spokesman for the Xinjiang regional higher people's court as saying.

The announcement came hours after state media said three people had been sentenced to die over the Tiananmen crash last October and underscores the tough approach authorities are taking to increasingly brazen and violent incidents.

The Tiananmen attack was one of several that have rocked China since last year, and which Beijing has blamed on Xinjiang separatists.

- 'Terror' crackdown -

The far-western region is the resource-rich homeland of the Uighurs and other groups, and periodically sees ethnic tensions and discontent with the government burst into violence.

In March a horrific knife assault at a railway station in the southern city of Kunming left 29 dead and 143 wounded.

Last month 39 people were killed, along with four attackers, and more than 90 wounded when assailants threw explosives and ploughed two off-road vehicles through a crowd at an Urumqi market.

Chinese courts, which are controlled by the ruling Communist Party and have a near-perfect conviction rate, frequently impose death sentences for terrorism offences.

The executions and sentencings are part of a crackdown that comes after Beijing vowed a year-long campaign against terrorism in the wake of the Urumqi market attack.

- 'Large-scale' campaign -

Shan Wei, a political scientist at the National University of Singapore's East Asian Institute, said Xinjiang has seen other similar "strike hard" campaigns in the past.

"But this time, it's much longer... usually it lasts one or two months," he said. "Now, it's one year. It's a large-scale campaign."

Exile groups say cultural oppression and intrusive security measures imposed by the Chinese government are the main causes of tension, along with immigration by China's Han ethnic majority, which they say has led to decades of discrimination and economic inequality.

Beijing, however, stresses ethnic harmony in Xinjiang and says the government has helped improve living standards and developed its economy.

One other person was given life in prison for the Tiananmen assault, said state broadcaster China Central Television (CCTV), citing the Intermediate People's Court in the Xinjiang capital Urumqi.

The three sentenced to death were convicted of "organising and leading a terrorist group and endangering public security with dangerous methods", according to Xinhua.

Four others were given prison terms ranging from five to 20 years, Xinhua said.

Both the agency and CCTV identified several of the accused with names that sounded Uighur, Xinjiang's largest ethnic group.

All three people in the car -- a man, his wife and his mother -- died in the attack, which saw their vehicle plough into crowds of tourists, killing two and wounding 40 other people before bursting into flames, authorities said at the time.

CCTV showed the eight accused -- two of them women -- sitting in a vast courtroom as prosecutors presented the evidence against them. An unidentified woman wearing a headscarf in the audience wiped away tears.

For the first time security camera video was broadcast of the attack, with CCTV showing a white SUV turning onto a pavement at high speed and barrelling into crowds of pedestrians, who scattered before it.

Tiananmen Square lies at the centre of Beijing and is bounded to the north by the former imperial complex known as the Forbidden City with a giant portrait of Communist China's founding father Mao Zedong hanging on its gate.

"If you do something within Xinjiang, most Chinese people won't know about that," Shan said.

"But if you do something in a major city -- for example in Beijing, Shanghai or Guangzhou -- that will be headline news. And that will be more effective to create terror among Han Chinese people."

Chinese authorities have long said that overseas-based terror groups including the Turkestan Islamic Party (TIP) and East Turkestan Islamic Movement (ETIM), influenced by Al-Qaeda, have inspired and even orchestrated violence in China from Central Asia, which borders Xinjiang.

Some experts question the influence of the TIP, a shadowy organisation that has released videos praising attacks in China but has yet explicitly to claim responsibility for them.