The exercises, involving ground troops and air forces, come amid growing instability in Afghanistan.

Chinese and Russian military forces are engaged in joint exercises in north-western China as ties grow between the two autocratic states amid uncertainty over instability in Afghanistan.

The exercises involving ground troops and air forces are due to continue through until Friday in the Ningxia Hui Autonomous region.

The region borders on Xinjiang, where China has detained more than one million Uyghurs and members of other Muslim minorities in what it calls a campaign against terrorism and extremism.

Xinjiang shares a narrow frontier with Afghanistan, and Beijing is concerned about violence spilling over its border if the Taliban take control in the country following the pullout of US and NATO troops.

While not part of a formal alliance, Russia and China have aligned their military and foreign policies largely in opposition to those of the US and its allies.

The official Xinhua News Agency said the exercises began on Monday and were presided over by Li Zuocheng, a member of the ruling Communist Party's Central Military Commission.

The exercise aims to "deepen the joint anti-terrorism operations between the Chinese and Russian militaries and demonstrate the firm determination and strength of the two countries to jointly safeguard international and regional security and stability", Xinhua said, citing Chinese and Russian officials.

"It reflects the new height of the China-Russia comprehensive strategic partnership of co-ordination for a new era and of the strategic mutual trust, pragmatic exchanges and co-ordination between the two countries," Xinhua said.

Russia has backed China in its claim to virtually the entire South China Sea, over which Beijing clashed with common rival the US at a high-level UN Security Council meeting on maritime security.

Australia has deployed hundreds of soldiers to Sydney to help enforce a Covid lockdown. A Delta outbreak which began in June has produced nearly 3,000 infections and led to nine deaths.

Australian Defence Force soldiers will undergo training on the weekend before beginning unarmed patrols on Monday. But many have questioned whether the military intervention is necessary, calling it heavy-handed.

The lockdown - in place until at least 28 August - bars people from leaving their home except for essential exercise, shopping, caregiving and other reasons. Despite five weeks of lockdown, infections in the nation's largest city continue to spread. Officials recorded 170 new cases on Friday.

Soldiers will join police in virus hotspots to ensure people are following the rules, which include a 10km (6.2 miles) travel limit. State Police Minister David Elliott said it would help because a small minority of Sydneysiders thought "the rules didn't apply to them".

Information provided by health officials indicates the virus is mainly spreading through permitted movement.

Australian police have issued a fresh appeal for help to find the remains of Peter Falconio, the British backpacker murdered in the outback 20 years ago.

The 28-year-old was shot dead when he and his girlfriend Joanne Lees were ambushed near Alice Springs in 2001. His body was never found. Australian man Bradley Murdoch was found guilty of his murder in 2005.

Despite pleas, he has refused to tell authorities where he disposed of Mr Falconio's body. The Northern Territory police renewed their search appeal on Wednesday, the 20th anniversary of Mr Falconio's disappearance.

They urged "anyone out there with any information" to come forward to police to help "assist Peter's family in gaining some sort of closure".

"We are thinking of Peter's family and friends on this anniversary and remain hopeful that such a milestone may jolt some information and progress the investigation," said Det Snr Sergeant Karl Day.

The head of MI5 is to urge the public to be as vigilant about threats from "hostile states" as from terrorism. These include disruptive cyber-attacks, misinformation, espionage and interference in politics - and are usually linked to Russia and China.

In a speech on Wednesday, Ken McCallum will say these "less visible threats... have the potential to affect us all". He will say these threats are affecting UK jobs and public services and could even lead to a loss of life.

The head of the Security Service wants to challenge the idea that activity by so-called "hostile states", usually taken to mean primarily Russia and China, only affects governments or certain institutions. Instead, he will argue, in an annual threat update, that the British public are not immune to the "tentacles" of covert action by other states.