The United States has advised airlines to follow Chinese rules for aircraft entering the country's new air defence zone over the East China Sea.
According to the BBC, it does not mean the US accepts China's requirements in the zone covering territory claimed by China, Japan, Taiwan and South Korea, but expects aircraft to observe the rules.
China wants all US carriers to notify authorities of their flight plans when entering the zone.
The new East China Sea Air Defence Identification Zone (ADIZ) was created last Saturday and covers around one million square miles of skies.
Reuters reports that the US, Japan and South Korea defied the rules this week and flew military aircraft through the area without notifying authorities.
"China's air force is on high alert and will take measures to deal with diverse air threats to firmly protect the security of the country's airspace," air force spokesman Shen Jinke told China's news agency Xinhua.
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