A university in Shanghai said on Friday it rejects FBI suspicions against a Chinese professor who previously worked at an American university that he might have shared top US defense secrets with China.

Li Rongxing, a former professor at Ohio State University (OSU), is a professor at Tongji University (TJU) with the College of Surveying and Geo-informatics, according to a TJU statement sent to the Global Times.

Li, a US citizen who grew up in China, was reportedly missing when FBI tried to determine whether Li shared defense secrets with the Chinese, the Columbus Dispatch reported on Tuesday.

In 2014, Li submitted a $36.9 million proposal to NASA for imaging work for a 2020 Mars mission, but he decided to withdraw from the project a month later.

He then resigned from his post as OSU's premier mapping expert. Jeff Grabmeier, a spokesman for OSU research said he couldn't say why Li left.

The OSU called on the FBI for the "unusual circumstances of Li's departure and the restricted and sensitive nature of some of his research."

However, Wu Weimin, a spokesman from TJU, told the Global Times Friday that Li quit his OSU job to look after his sick parents in China.

TJU's statement added that the reports were ill-founded.

Li, who used to be a visiting professor at TJU while working at OSU, started working at TJU as a professor earlier this year, Wu said.

"Li, who completed undergraduate and graduate studies at our university, has contributed immensely to TJU. We do not believe he has shared any secrets," Wu said.

"Li's US lawyer said the investigation had already ended," Wu told the Global Times.