Russia has restarted sales of its advanced weapons to China for the first time since it virtually suspended all transactions in 2004, amid concerns that Beijing would copy Moscow’s technology. Japanese government officials fear that Russia’s move could destabilise the delicate security situation in the region.

China and Russia agreed this week that Beijing will buy 24 advanced Sukhoi Su-35 fighters, four of which will be delivered by new year. The other aircraft, according to the $2bn deal, will be with China within three years. Russia has also agreed to deliver its S-400 anti-aircraft missile system as soon as 2018.

The Su-35 is an advanced Russian stealth combat fighter, with enhanced avionics and a longer-range flight capability. It is capable of aerial combat and striking ground and maritime targets.