China says it has begun introducing its J-20 stealth fighter jets into combat units, in a potentially major upgrade of its air force capabilities.

Air force spokesman Shen Jinke said in a statement released on the service's official microblog Friday that the move boosts China's ability to carry out the "sacred mission" of defending its sovereignty, security and territorial integrity.

First flown in 2011, the J-20 is China's answer to fifth-generation jets such as the U.S. F-22 and F-35.

It made its formal debut at a 2016 air show in southern China and last year was featured in a military parade marking the 90th anniversary of the founding of the People's Liberation Army.

The plane was developed domestically but is believed to still rely on Russian engines for power.