Chinese Foreign Ministry spokesman Geng Shuang sternly criticized Washington for supporting Japan’s sovereignty over the East China Sea’s Senkaku Islands, demanding the U.S. “exercise prudence and stop making wrong remarks so as not to complicate relevant issues.”

The comment followed a weekend visit to the United States by Prime Minister Shinzo Abe of Japan, who has made national defense a top priority of his administration. In addition to Geng’s rejection of President Donald Trump’s support for longtime ally Japan, state media republished reports of Chinese military excursions near the Senkakus occurring after Secretary of Defense James Mattis asserted the Trump administration’s position on the Senkakus in Japan.

“China is gravely concerned about and firmly opposed to relevant comments by Japan and the United States,” Geng told reporters at the ministry’s regular briefing on Monday. “Diaoyu Dao and its affiliated islands are China’s inherent territory,” he said, using the Chinese name for the islands, “No rhetoric or actions, from whomsoever, will change the fact that Diaoyu Dao belongs to China or waver China’s resolve and determination to uphold its national sovereignty and territorial integrity.”

“We are firmly against Japan’s attempt to try to gain the US support for its illegal territorial claims in the name of the so-called mutual defense treaty. Japan and the US should exercise prudence and stop making wrong remarks so as not to complicate relevant issues or bring negative impact on regional peace and stability,” Geng concluded.

Geng went on to make similar assertions about Philippine and Vietnamese territory in the South China Sea: “China has indisputable sovereignty over the South China Sea islands and their adjacent waters.”

The state-run publication Xinhua republished on its English-language homepage Monday a week-old article on the Senkaku Islands, as well, in an apparent attempt to remind the United States that the Chinese military is willing to maintain a presence in the region.

“China conducted a new round of regular patrol in the territorial waters of the Diaoyu Islands on Monday, showing the world its firm will and determination to safeguard its national sovereignty,” the article read. The piece attributed “the decaying U.S. credibility in East Asia” under President Barack Obama on the previous administration’s insistence on supporting its ally Japan.

The drill in question consisted of three Chinese warships sailing within 12 nautical miles of the islands, the United Nations-designated limit of where a nation’s sovereign maritime territory ends. Japan had reported 36 drills of this nature in 2016 alone.

The Senkakus are uninhabited islands in the East China Sea believed to hold vast fossil fuel resources. While they are the sovereign territory of Japan, China claims to be the rightful master of the maritime region and has spent the past four years aggressively attempting to reclaim it.

In 2013, China announced the establishment of an Air Defense Identification Zone (ADIZ) over the islands, which would require any non-Chinese aircraft to identify themselves to Beijing while passing through — essentially forcing Japanese planes to tell China when they were flying in Japanese territory.

Japanese and American aircraft largely disregarded the ADIZ, as Japan had long established one over the islands. China appears to have largely ceased attempting to enforce it after President Obama issued a warning that the U.S. is treaty-bound to attack China if Beijing orders a military assault on any Japanese aircraft in the Senkakus.

On his first trip abroad as Secretary of Defense, Mattis repeated this warning. “I made clear that our long-standing policy on the Senkaku Islands stands,” Mattis said following a meeting with his Japanese counterpart, Tomomi Inada. “The US will continue to recognize Japanese administration of the islands and as such Article 5 of the US-Japan Security Treaty applies.”

Japan, meanwhile, has responded to growing tensions by approving the largest defense budget in its history at the end of 2016, reaffirming Prime Minister Abe’s prioritizing of Japan’s Self-Defense Forces. Japan’s post-World War II Constitution prohibits it from maintaining a standing military.