Emboldened by a visit from Secretary of State Rex Tillerson that Beijing has celebrated as a success, China has lodged a protest with the United States over a B-1 bomber flying within an Air Defense Identification Zone (ADIZ) set over Japan’s Senkaku Islands in the East China Sea.

China claims the Senkaku Islands – resource-rich but uninhabited rock formations within Japan’s exclusive economic zone – as its own and established an ADIZ over them in 2013. The ADIZ requires that any aircraft flying over the Diaoyu, as China calls them, identify itself to Beijing. This would require Japanese planes flying in Japanese airspace to keep China informed of their whereabouts at all times, something Tokyo has called “totally unacceptable” and the Obama administration vowed to dismiss as illegal.

The Chinese military warned an American bomber flying within the ADIZ Sunday – present in the region to participate in joint exercises with the South Korean military – to identify itself as the ADIZ requires. CNN reports that the Chinese military told the pilots of the American aircraft that “they were illegally operating in Chinese airspace” and demanded they leave.

“Pacific Air Forces… did not recognize the Chinese Air Defense Identification Zone (ADIZ) when it was announced in November of 2013, and does not recognize it today,” U.S. Pacific Air Forces spokesman Maj. Phil Ventura told CNN. “The ADIZ has not changed our operations.” The bombers in question completed their operations in the region.

While Chinese Foreign Ministry spokeswoman Hua Chunying refused to discuss the specifics of the encounter on Thursday, she issued a firm defense of the ADIZ: “It is the legitimate right of a sovereign state to demarcate ADIZs. The US, who also has its ADIZs, should respect the right of other countries to establish ADIZs.”

China established the ADIZ in November 2013 with the demand that “all aircraft must notify Chinese authorities and are subject to emergency military measures if they do not identify themselves or obey orders from Beijing.” At the time, the Japanese government called the move “totally unacceptable” and, soon after the declaration, Washington weighed in rejecting the territorial claim.

“The policy of the United States is clear–the Senkaku Islands are administered by Japan and, therefore, fall within the scope of Article 5 of the U.S.-Japan Treaty of Mutual Cooperation and Security,” President Barack Obama said in April 2014 in answer to a media request to clarify the issue. Article 5 of the post-war treaty in question requires the United States to use its military to defend the integrity of Japan’s territory from foreign invasion or usurpation. Should the Chinese attack a Japanese aircraft within the ADIZ for not identifying itself to Beijing, the United States would be treaty-bound to retaliate and engage in military action with China.

The Chinese government has largely abandoned attempts at enforcing the ADIZ following President Obama’s threat to use military force.

The Japanese, meanwhile, have exercised their sovereignty over the region, even sometimes to the benefit of China. In a rare gesture of diplomatic solidarity with China, the Japanese Coast Guard rescued Chinese sailors whose ship sank near the Senkaku Islands in August 2016, receiving statements of gratitude from the Chinese Communist Party leaders.

The Trump administration appears to have no intention of overturning the Obama-era policy on the East China Sea ADIZ. During his visit to Japan in February, Secretary of Defense James Mattis told reporters that he told his Japanese counterparts that “our long-standing policy on the Senkaku Islands stands – the US will continue to recognize Japanese administration of the islands and as such Article 5 of the US-Japan Security Treaty applies.”

The latest Chinese protests on the ADIZ follow what Beijing has heralded as an extremely cordial meeting between Secretary of State Tillerson and Chinese President Xi Jinping. The Chinese appear to be setting the table for introducing a discussion of the ADIZ to upcoming in-person talks between Xi and U.S. President Donald Trump.

In its analysis of Tillerson’s visit last week, the Chinese government newspaper People’s Daily praised Tillerson for “endors[ing] the new model of major-country relations, which was proposed by Chinese President Xi Jinping.”

“In his China debut, Tillerson has received criticism for embracing the new model, but it is a win-win for both countries,” the Daily argued, “as well as for the global community, if what many experts describe as the world’s most important bilateral relationship is guided by a common understanding and continues to develop in a direction featuring no conflict, no confrontation, mutual respect, and win-win cooperation for many years to come.”