Beijing issued a warning to a US Air Force bomber when it was flying above the East China Sea on Wednesday (22 March), US officials told multiple media outlets.

The bomber was thought to be on a routine mission in international airspace when it was warned by the Chinese forces.

Two unnamed officials have confirmed the encounter to Fox News while the CNN cited a senior defence official to corroborate the account.

The US pilots were told by the Chinese military that they were illegally operating in the airspace when the military aircraft was flying near South Korea. However, the pilots did not deviate from the actual path despite the warning, it was reported.

It is still unclear whether it was the US's Air Force's same B-1B Lancer bomber, which carried out the sortie above the Korean peninsula as part of the ongoing training exercises with South Korea.

China had earlier unilaterally claimed the Air Defence Identification Zone (ADIZ) in the East China Sea above a hotly contested region, which is claimed by both Japan and South Korea. Beijing's previous move had sparked sharp responses from both the countries when the step was announced.

A US Air Force B-1B bomber flies over Osan Air Base in Pyeongtaek, South Korea Reuters

Though China demands prior notification from aircraft flying in the ADIZ, US and other powers do not recognise the requirement and consider the airspace international. "Pacific Air Forces ... did not recognise the Chinese Air Defence Identification Zone (ADIZ) when it was announced in November of 2013, and does not recognise it today. The ADIZ has not changed our operations," US Pacific Air Forces spokesperson Major Phil Ventura was quoted as saying.