In a message published Friday by the State Department, Secretary Mike Pompeo wrote: “On behalf of the people of the United States, I offer congratulations to the people of China as you celebrate your National Day on October 1.” He added: “The United States wishes the people of China happiness, health, peace and prosperity in the year to come.”

But the message came amid not only a global trade war between the two top economic competitors, but also frictions in the South China Sea, where Nimitz-class, nuclear-powered supercarrier USS Ronald Reagan recently defied Beijing’s territorial claims.

“The U.S. side loves to take petty actions just before China’s major holidays, but history has proved that no petty actions can affect the overall development of the Chinese military and the nation,” Chinese Defense Ministry spokesperson Senior Colonel Ren Guoqiang told a press briefing Sunday. “The Chinese military will methodically fulfill its duties and safeguard national sovereignty, security and development interests, as well as peace and stability of the region and the world.”

China has vast claims across the traffic-heavy, resource-rich South China Sea, disregarding the competing claims of other regional states as it stepped up the construction of military infrastructure on disputed islands and islets. The U.S., already host to an estimated 279 military installations in the Asia-Pacific region, has condemned this practice and asserted its own presence.

One way in which the Pentagon has sought to do so is through so-called “freedom of navigation” operations. The practice was outlined in the 1982 United Nations Convention on the Law of the Sea, a treaty ratified by China, but not the U.S.

Ren warned in response to the latest move: “We demand the U.S. side respect the security concerns of various nations from the region and add positive energy to South China Sea’s peace and stability.” He also hit out at a report issued Tuesday by the Congressional Research Service.

“China’s navy is viewed as posing a major challenge to the U.S. Navy’s ability to achieve and maintain wartime control of blue-water ocean areas in the Western Pacific—the first such challenge the U.S. Navy has faced since the end of the Cold War—and forms a key element of a Chinese challenge to the long-standing status of the United States as the leading military power in the Western Pacific,” the report read.

Ren said the wording “goes to show the arrogance and prejudice, as well as the zero-sum and Cold War mentalities of some U.S. officials.” He stated that “such actions are ridiculous, erroneous and dangerous, and the Chinese side resolutely opposes them.”

Meanwhile, the U.S. and China have yet to settle their disputes on the economic front, either. President Donald Trump devoted a portion of his address Tuesday to the United Nations General Assembly to touting his strict stance in laying out tariffs against China and accusing Beijing of dishonest trade practices.

“The American people are absolutely committed to restoring balance to our relationship with China,” Trump said. “Hopefully, we can reach an agreement that would be beneficial for both countries. But as I have made very clear, I will not accept a bad deal for the American people.”

Chinese President Xi Jinping did not attend this year’s international gathering in New York. Instead, he was represented by Chinese Foreign Minister Wang Yi, who called for “dialogue and consultation” with the U.S. that was “based on mutual respect, equality and honoring one’s word with action.”

“Given the size of our economies and the level of interdependence, the so-called ‘decoupling’ or ‘shutting the door to each other’ is just like an attempt to build castles in the air,” Wang told a reception at the U.S.-China Business Council. “It is neither sensible nor realistic.”