U.S. Pacific Command head Admiral Harry Harris vowed to prevent China from “closing down” the South China Sea in a speech on Wednesday, confirming that Australia would allow the U.S. to fly fighter planes out of its territory to help keep the region free.

The comments prompted a stern rebuke from Chinese Foreign Ministry officials and Chinese state-run propaganda publications, which have expressed increasingly loud concerns that incoming President-elect Donald Trump will be less open to negotiate with the Communist government than his predecessor, President Barack Obama.

“We will not allow a shared domain to be closed down unilaterally no matter how many bases are built on artificial features in the South China Sea,” Harris said in Sydney this week. “We will cooperate when we can but we will be ready to confront when we must.”

He noted that America is currently facing “significant challenges… posed by a revanchist Russia and an increasingly assertive China,” particularly in the South China Sea, where China claims both international waters and the sovereign territories of Vietnam, the Philippines, Brunei, Malaysia, and Taiwan. The Permanent Court of Arbitration at the Hague found China’s claims to the region invalid, though China vowed to ignore the international tribunal entirely and new Philippine president Rodrigo Duterte has so far agreed not to mention it in bilateral talks.

“I’ll be blunt in saying that the global operating system that created the Indo-Asia-Pacific economic miracle is coming under pressure from revisionist powers,” he said, adding that there was “no room for subtlety” in challenging these “revisionist powers,” China and Russia.

To meet those challenges, Harris announced that Australia had agreed to allow the United States to fly missions out of its territory using what the Sydney Morning Herald calls America’s “deadliest fighter plan,” the F-22 Raptor.

The Chinese Foreign Ministry has replied by once again warning the United States that having a presence in the South China Sea is a direct challenge to Beijing. “We hope the United States can abide by its promises on not taking sides on the sovereignty dispute in the South China Sea, respect the efforts of countries in the region to maintain peace and stability in the South China Sea region and do more to promote peace and stability there,” said spokesman Geng Shuang, Reuters reported.

Geng added a warning to the incoming Trump administration not to challenge the “One China” policy, which states that the United States should not acknowledge sovereign nations like Taiwan, which Beijing considers a runaway province. “China opposes official and military relations between the United States and Taiwan in any form, Geng said,” the People’s Daily reports.

“We urged the United States to stick to the one-China policy and three Joint Communiques between China and the United States, and to deal with the Taiwan issue in a prudent and discreet manner to prevent China-U.S. ties from being disturbed,” Geng reportedly said.

The Global Times, a Beijing-run media outlet that the government often uses to print more belligerent opinions than those the Foreign Ministry publishes, ran an editorial on Wednesday calling for China to take initiative on colonizing the South China Sea before Trump takes office.

“It is high time for China and its rival claimants in ASEAN [Association of Southeast Asian Nations] to make major progress in the South China Sea disputes,” the article argued. “Stability and cooperation in the South China Sea can be achieved without interference from external countries. This job had better be done before Trump could make choppier waves in the region.” The article goes on to call Trump a “political rookie” whose “aggressive posturing against China has generated a lot of uncertainties.”