Forty "rioters" were killed in China's far-western Xinjiang region following a series of explosions last Sunday, the worst incident of violence in months, the regional government has said after a four-day news blackout.

Residents on Friday described heavy security in place days after the violence.

Six civilians, two police officers and two auxiliary police were also killed in the attacks in Xinjiang's Luntai county, with 54 civilians injured, the regional government's news portal Tianshan said late Thursday.

Two "rioters" were captured, it added, while the main suspect, whose name was given as Mamat Tursun, was shot dead.

The violence took place just two days before the sentencing of prominent Muslim Uighur scholar Ilham Tohti, who was on trial on charges of separatism.

Chinese state media had previously only stated that two people had been killed in the incident. The ruling Communist Party tightly restricts access to the restive region, and information is difficult to independently verify.

Such a delay in the release of details is not uncommon.

Staff at hotels in Luntai county contacted by AFP described a continuing heavy security presence.

"Security forces are still in the street," said one receptionist.

A woman who answered the phone at another inn also gave an account of security out in force, and that business had suffered as "lots of people don't come these days".

- 'Organised and serious' attack -

Tohti, a former university professor who has been critical of Beijing's policies in the vast western region, was sentenced to life in prison on Tuesday.

The United States, the European Union, and several human rights groups have called for the release of Tohti, 44, whose prosecution risks silencing moderate Uighur voices and cutting off the possibility of dialogue, analysts say.

Critics also warned his conviction could add to tensions in the restive region.

Teng Biao, a leading human rights lawyer and friend of Tohti, wrote this week that rather than a life sentence, the academic should be awarded a Nobel prize.

"The Chinese communist authorities, with their excessive violence, have created hostility, division and despair in Xinjiang and Tibet," Teng wrote in The Guardian newspaper.

"Tohti has denounced violence and devoted himself to bridging the divide and promoting understanding and tolerance."

Beijing on Friday dismissed the possibility that the Tohti verdict could negatively impact China's relations with other countries.

"We should not let these small things affect our bilateral relations," Chinese foreign ministry spokeswoman Hua Chunying said.

The Global Times, a tabloid run by the official Communist Party mouthpiece People's Daily, said in a column on its editorial page that Tohti's case should be seen as warning to anyone trying to break China apart.

"Chinese separatists must be fully aware of the red line drawn by the Chinese constitution and criminal law," it said.

"Tohti could serve as a lesson for them to realise what price they have to pay if they continue their dangerous pace."

According to the Tianshan report, the "organised and serious" attack comprised four explosions that took place Sunday evening, targeting two police stations, an outdoor market and a shop.

Among the 54 civilians injured were 32 members of China's mostly Muslim Uighur minority and 22 Han Chinese, it said.

The 40 "rioters" killed had either blown themselves up or were shot dead by police, Tianshan said.

- Escalating violence -

Police said that Mamat Tursun, the alleged ringleader of Sunday's attack, had been "gradually developing into an extremist" since 2003 and had "called on other people to join his terrorist group when working on construction projects", according to the official Xinhua news agency.

In the past year, escalating violence between locals and security forces in Xinjiang -- the traditional homeland of the Uighurs -- has claimed more than 200 lives and prompted Beijing to launch a security crackdown.

Among the most shocking attacks was a May assault on a market in the regional capital Urumqi, where more than 30 people were killed.

Beijing blames ongoing unrest in the region on organised terrorists seeking independence from China, while rights groups say cultural and religious repression of Uighurs has stoked violence.

China's supreme court on Sunday distributed new wide-ranging guidelines on prosecuting terrorism cases.

"Making and showing banners and other material of religious extremism will be criminalised," the state-run Xinhua news agency said in a summary of the regulations.

The court also said that the use of insults such as "religious traitor" and "heretic" could lead to criminal conviction.

Xinjiang, a resource-rich region which abuts Central Asia, is home to about 10 million Uighurs, who mostly follow Sunni Islam.

Timeline of unrest related to China's Xinjiang region
Beijing (AFP) Sept 26, 2014 - Forty "rioters" have been killed in China's Xinjiang after a series of coordinated explosions, according to authorities, who have blamed "terrorists" for a string of incidents in the largely Muslim region.

Here is a chronology of key events related to the restive region since 2009:

2009

June 25 -- Two Uighur factory workers are reported killed and dozens injured in a huge brawl with Han Chinese in Shaoguan, in the southern province of Guangdong.

July 5 -- Hundreds, perhaps thousands, of Uighurs riot in the Xinjiang capital Urumqi after security forces move in on a protest over the Shaoguan incident.

July 7 -- The government says nearly 200 people died in the unrest, with more than 1,600 injured and hundreds arrested. Eventually at least 26 are reportedly sentenced to death.

September 2 -- Han residents of Urumqi protest for days over a wave of syringe stabbings that the government eventually says had nearly 500 victims, blaming "ethnic separatist forces".

2011

July 18 -- Police kill 20 protesters in clashes in Hotan, southern Xinjiang, exiled Uighur groups say. State media say police fired on demonstrators who attacked a police station, killing one officer.

September 15 -- Courts in Xinjiang sentence to death four Uighurs over the July incidents.

December 28 -- Police in Pishan kill seven "terrorists" in a hostage standoff that left one officer dead. State media calls them terrorists engaged in a "holy war".

2012

February 28 -- Rioters armed with knives kill at least 10 people in Yecheng, while police shoot two of the attackers dead, state press say. One man is later sentenced to death.

2013

April 23 -- Gunfights in Bachu leave 15 police and community workers and six "terrorists" dead. Two men are later sentenced to death.

June 26 -- At least 35 people are killed when, according to Xinhua, "knife-wielding mobs" attack police stations and other sites in Lukqun before security personnel open fire. Three people are later sentenced to death.

October 28 -- Three members of the same Xinjiang family crash their car into tourists in Tiananmen Square in Beijing, the symbolic heart of the Chinese state, killing two, before setting it on fire and dying themselves, according to authorities who call it a terrorist attack. Three people are later executed.

December 16 -- 14 Uighurs and two police officers are killed in Shufu county. Authorities describe the slain Uighurs as members of an extremist group, but campaigners say police raided a house where a family was preparing for a wedding, with six women among those killed.

2014

January 15 -- A prominent Uighur academic and critic of government policy, economics professor Ilham Tohti, is detained by police and later charged with "separatism".

January 25 -- A total of 12 people are killed in Xinhe, six in explosions and six shot dead by police dealing with "violent incidents", a government-run news portal says.

March 1 -- Knife-wielding assailants kill 29 people and wound more than 130 at Kunming train station in Yunnan province, more than 1,600 kilometres (1,000 miles) from Xinjiang. Officials blame separatists from Xinjiang.

April 30 -- Assailants armed with knives and explosives attack a rail station in Urumqi, killing one person and wounding 79, on the final day of a visit by President Xi Jinping.

May 22 -- 39 people are killed, along with four attackers, and more than 90 wounded when assailants throw explosives and plough two vehicles through a market in Urumqi, state media say.

June 16 -- Authorities execute 13 people and send more than 100 to jail in a public mass sentencing on mostly terrorism-related offences in Xinjiang.

July 28 -- 37 civilians and 59 "terrorists" are killed and another 13 civilians wounded in an attack on a police station and government offices in Yarkand. Police arrest 215 people in connection with the incident, according to state media.

July 30 -- Jume Tahir, the government-appointed head of the Id Kah mosque in Kashgar, the largest in China, is killed after leading morning prayers. Police shoot dead two alleged assailants and capture a third.

August 1 -- Police in Hotan shoot dead nine suspected terrorists and capture one after discovering the group in a cornfield, according to state media.

September 21 -- A total of 40 "rioters", six civilians and four police are killed in Xinjiang's Luntai county after a series of coordinated explosions at police stations, a market and a shop, authorities say days later.

September 23 -- Tohti is sentenced to life in prison for "separatism."