The Foreign Ministry confirmed on Wednesday that the Chinese delegation's absence at the International Astronautical Congress in Washington is due to visa problems, urging the United States not to "weaponize" visas to hinder normal international cooperation.

The US did not issue visas for the delegation in time, ministry spokeswoman Hua Chunying said at a daily news conference, adding that in July, China had presented to the US the list of attendants and that visa interviews took place in the US embassy on Oct 12.

But the head of delegation still did not have his visa as the congress began, Hua said. "This caused the Chinese delegation to be unable to attend the opening of the International Astronautical Congress," Hua said.

Several other Chinese delegates also did not get visas, she added.

China has always championed multilateral cooperation in space exploration and actively participates in the conference every year, Hua said.

"I miss an important space agency in this panel. Where is China?" Attendees at a plenary meeting of the weeklong congress brought the question to the top of the panel voting system and demanded an answer.

At the opening ceremony, US Vice-President Mike Pence claimed that his country would only "work closely with likeminded, freedom-loving nations, as we lead mankind into the final frontier."

His politicized remarks triggered aversion from the audience as about 200 people from the US astronautical community signed a letter condemning Pence, whose inclusion, they said, was at odds with the congress's mission of global collaboration.

The visa problem encountered by the Chinese delegation is only the "tip of an iceberg", Hua said.

For quite a while, she noted, the US has been denying visas, delaying the processing of visa applications and revoking long-term visas for Chinese scholars, students, entrepreneurs and scientists and even searching and harassing them.

Such moves have thwarted normal people-to-people exchange between China and the US and infringed upon the safety and lawful rights and interests of the Chinese personnel involved, she said.

The US has repeatedly disregarded international obligations and disrupted normal international exchanges, Hua said, asking Washington to sincerely reflect on and earnestly correct its wrongdoing.

Xinhua contributed to this story.