HONG KONG (Reuters) - The U.S. State Department said Hong Kong’s leader, Carrie Lam, rejected a request last year to surrender a fugitive into the custody of the United States, at China’s behest.

Hong Kong Chief Executive Carrie Lam attends the opening ceremony of Art Basel Hong Kong in Hong Kong, China March 27, 2018. REUTERS/Bobby Yip

In an annual report on the Asian financial hub this week, the State Department said last October’s rejection was the first such instance since the former British colony returned to Chinese rule in 1997.

Hong Kong has a formal extradition agreement with the United States but not with China, although the latter has handed over criminal suspects on an ad hoc basis through the years.

The refusal was “at the behest of the (Chinese) central government,” the State Department said, adding that the fugitive was later released into Chinese custody “on the basis that the central government was pursuing a separate criminal action”.

It added, “The central government has provided no information as to the disposition of its own case.”

Hong Kong’s “one country, two systems” arrangement guarantees it a high degree of autonomy not enjoyed in mainland China, including independent judicial power and law enforcement.

But police in China’s bordering southern province of Guangdong have sent at least 175 suspects to authorities in Hong Kong since 2000, state media said last year.

The U.S. report did not name the fugitive, or detail the crime, but Hong Kong media said the individual was Iat Hong, a computer hacker and Macau resident charged by U.S. authorities with stealing confidential information from U.S. law firms and trading on it for profit.

Reuters was unable to immediately trace contact details for Hong.

A spokeswoman for the U.S. consulate in Hong Kong gave no further details when contacted by Reuters, and declined to confirm if the individual was Iat Hong.

Hong’s rejected extradition request, however, was mentioned in a U.S. Department of Justice letter this year in a separate graft case involving a former senior Hong Kong official, Patrick Ho.

Hong’s “lengthy, cumbersome extradition application” was rejected after nearly 10 months of proceedings in Hong Kong, the letter said.

“Hong ... has not been - and it appears never will be - extradited,” it added.

Lam’s office, and the Department of Justice, declined to make any immediate comment.

Pro-democracy lawmaker James To said the case undermined public confidence in Hong Kong’s autonomy and urged the city’s leader to explain the decision.

Young people in Hong Kong have expressed frustration at the perceived creeping influence of Communist Party rulers in Beijing over the city’s culture and freedoms.

In Beijing, a foreign ministry spokeswoman said she had no specific understanding of the case, but stressed China fully supported Hong Kong’s autonomy under the “one country, two systems” arrangement.

However the U.S. report had made “irresponsible comments” and China was resolutely opposed to it, the spokeswoman, Hua Chunying, told a regular media briefing.

The U.S. report also mentioned signs of overreach by Chinese authorities in Hong Kong.

“Central government authorities ... issued public statements that diluted the concept of ‘high degree of autonomy’ and the freedoms contemplated in the Basic Law,” it said, referring to the city’s mini-constitution.

(Refiles to capitalize department name in headline)