The top U.S. official responsible for relations with Taiwan said Tuesday that Chinese pressure on an American governor to cancel a visit to the island was "unacceptable," and inconsistent with Beijing's desire to improve ties with Taipei.

In December, Missouri Gov. Jay Nixon scrapped plans to visit Taiwan after a Chicago-based Chinese diplomat warned that the trip could imperil a project by China to turn the St. Louis airport into a hub for Chinese cargo in the United States.

Over the previous two years, eight American governors had visited the island, which, despite having no formal diplomatic relations with Washington, remains an important American security partner and key destination for U.S. exports.

Speaking to reporters in Taipei, American Institute in Taiwan Chairman Ray Burghardt called China's actions "absolutely unacceptable."

"My impression is that most American politicians, American governors, they don't like to be pushed around that way," he said.

Burghardt said China's actions appeared to be at odds with the rapid improvement in relations across the 100-mile- (160-kilometer-) wide Taiwan Strait that have taken place since Taiwanese President Ma Ying-jeou jettisoned his predecessor's support for formal independence upon taking office 2 1/2 years ago.

"It's ... inconsistent with all their professions of desire to improve cross-strait relations to treat Taiwan that way," Burghardt said. "I think it's a serious matter."

Taiwan and China split amid civil war in 1949. Beijing still claims the democratic island as part of its territory and attempts to limit any activity that might appear to give it the appearance of a sovereign state.

Washington transferred its recognition of China from Taipei to Beijing in 1979. AIT, which Burghardt oversees from offices in Washington and Honolulu, was established the same year as the de facto American Embassy on the island.

Nixon's aborted visit to Taiwan focused on selling $600 million worth of Missouri agricultural products to Taiwanese consumers. He originally said the trip's cancellation was due to "travel challenges," but later acknowledged that Chinese pressure had played a role.