Diplomatic tensions between China and the United States continued to climb Wednesday, when Chinese officials accused the United States of having “weaponized” the visa process after a top Chinese official was unable attend a major international space conference being held in Washington.

A spokesperson for the Chinese Foreign Ministry told reporters in Beijing that Wu Yanhua, the deputy head of the China National Space Administration, was not able to obtain a visa, and therefore was not able to attend, according to the Associated Press.

In a statement released Thursday morning, State Department Spokesperson Morgan Ortagus said the U.S. “rejects the Chinese Foreign Ministry’s unfounded and baseless characterization of U.S. visa policies toward China. We cannot discuss individual visa cases since visa records are confidential under U.S. law, but we can confirm that the Chinese delegation is in attendance at the conference.”

In an interview with The Washington Post, Vincent Boles, the co-chair of the local organizing committee for the conference, known as the International Astronautical Congress, said organizers had been working with officials from China for two years to make sure their officials would be able to navigate the various bureaucracies needed to receive the proper clearances.

Working with the U.S. State Department, the American Institute of Aeronautics and Astronautics (AIAA), which also helped organize the conference, reached out to Chinese officials very early in the process, asking them to submit the names of officials who would want to attend, said Daniel Dumbacher, the institute’s executive director.

Knowing how difficult gaining the visas would be, the group followed up repeatedly, but China did not forward the first group of names until late spring, some six months after the AIAA local organizing committee had asked for them. And the last group of names did not arrive until just a few weeks ago, Dumbacher said.

Despite the delays, the organizers said that a top Chinese official, Tian Yulong, and a delegation of five staff members were granted visas and planned to arrive for the conference on Wednesday, according to an email reviewed by The Post that was sent to conference organizers by Chinese officials.

“We work very hard to ensure the international involvement, participation and flavor of the International Astronautical Congress,” Dumbacher said. The group “took these requests very seriously. We took the challenge very seriously."

Boles said that the delay was caused when the conference received required paperwork “extremely, extremely late. And, of course, that puts [the State Department] in the bind of trying to administer visas.”

The group also worked with Russia, the local organizers said, and Sergei Krikalev, executive director of piloted spaceflights at Roscosmos, the Russian space agency, is attending the conference. More than 60 Chinese citizens were also in attendance, Dumbacher said. Having representation from as many countries as possible is a core value of the conference and is a way to showcase how space often transcends geopolitical tensions, according to organizers.

“The United States recognizes the importance of space cooperation and has encouraged very broad participation and attendance at this year’s IAC,” said Ortagus, the State Department spokesperson. She noted that the U.S. mission to China has issued more than 1.3 million visas in the last fiscal year, and that the U.S.'s offices in China “are some of the largest visa issuing posts in the world.”

The tension comes as the United States increasingly sees space as a war-fighting domain and is trying to stand up a Space Force to stem advances by potential adversaries such as China and Russia. In a speech earlier this year, Vice President Pence called for NASA to dramatically speed up its plan to return astronauts to the moon, casting it as part of a great-power competition with China, which landed a spacecraft on the far side of the moon, a historic first, in January.

“Make no mistake about it: We’re in a space race today, just as we were in the 1960s, and the stakes are even higher,” Pence said in a speech in March. China’s lunar efforts “revealed their ambition to seize the lunar strategic high ground and become the world’s preeminent spacefaring nation.”

Scott Pace, the executive secretary of the National Space Council, told The Post that U.S. officials are wary of cooperating with China in space the way they do with other nations, including Russia, which flies NASA’s astronauts to the International Space Station.

“Looking at Chinese behavior in other shared domains — the South China Sea, cyberspace — they’ve given us pause for concern,” he said. “And so looking out in space, it’s hard to imagine that they will behave any better than they’d behaved in other areas where they felt that their national interests are at stake.”

Earlier this month, the Trump administration said it would restrict visas for Chinese nationals suspected of being involved in human rights abuses of Uighur Muslims and other minorities. China condemned the move, saying it “violates the basic norms governing international relations,” CNN reported.

The absence of top officials from the China National Space Administration was noted at the conference, particularly at a panel where the heads of the space agencies from India, Russia, Japan, Canada, Europe and the United States gathered on Monday. In the conference program, Yanhua was listed as “invited.”

Asked about the reported absence of the Chinese space agency leaders, NASA Administrator Jim Bridenstine said, “I know we invited them, and I was anticipating them being here.”

Staff Writer Carol Morello contributed to this report.

This story has been updated.