China has joined Russia in opposing further Nato expansion as the two countries move closer together in the face of Western pressure.

Moscow and Beijing issued a statement showcasing their agreement on a raft of issues during a visit by Russia's Vladimir Putin for the Winter Olympics. Mr Putin claims Western powers are using the Nato defence alliance to undermine Russia.

It comes amid tensions over Ukraine, which he denies planning to invade. Some 100,000 Russian troops remain at the border with Ukraine, which is a former Soviet republic. Mr Putin, who has written that Russians and Ukrainians are "one nation", has demanded that Ukraine be barred from joining Nato. While the lengthy joint statement did not refer directly to Ukraine, the two countries accused Nato of espousing a Cold War ideology.

The talks, which the Kremlin said were "very warm", were held ahead of the Games opening ceremony. It was the first time the leaders have met face-to-face since the start of the pandemic. "Friendship between [Russia and China] has no limits, there are no 'forbidden' areas of cooperation,"

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.