HONG KONG (Reuters) - A U.S. congressional panel has warned of an “alarming” rise in China’s interference in Hong Kong, noting fears over the former British colony’s continued role as a global financial hub.

Riot police block a street during a standoff with protesters outside China Liaison Office in Hong Kong, China November 6, 2016. REUTERS/Bobby Yip

In its annual report to Congress on Wednesday, the bipartisan U.S.-China Economic and Security Review Commission highlights the “chilling” abduction and detention of five booksellers based in Hong Kong as well as pressure on media and academic freedoms.

Britain handed Hong Kong back to China in 1997 under a “one country, two systems” agreement that ensures its freedoms, independent legal system and wide-ranging autonomy remain intact.

The commission, in a detailed 33-page section, urges a fresh probe from the State Department into Hong Kong’s autonomy and freedoms, as well as continued congressional oversight.

“Hong Kong’s traditional standing as a global financial hub has significant economic implications for the United States, as U.S. trade and investment ties with Hong Kong are substantial,” the report notes.

It says the booksellers’ detentions - including two foreign nationals and one who was abducted inside Hong Kong - broadened domestic fears of mainland encroachment and sparked a record turnout in September’s legislative election.

“This incident has threatened the maintenance of the ‘one country, two systems’ framework and led some observers to question Hong Kong’s status as a leading global financial hub,” the report warns.

“The election took place against the backdrop of an alarming rise in mainland interference in Hong Kong.”

U.S. senators Marco Rubio and Tom Cotton also introduced a bill that would freeze U.S.-based assets and ban U.S. entry of those responsible for the “surveillance, abduction, detention, or forced confessions of certain booksellers and journalists in Hong Kong”, according to a statement on Rubio’s senate website.

In Beijing, Chinese Foreign Ministry spokesman Geng Shuang said Hong Kong was an internal matter for China and no foreign country had the right to interfere.

“In order to try to split the country, some forces have openly sought foreign support,” Geng told a daily news briefing.

“Those who attempt to use foreign forces to achieve their own political goals will not succeed.”

The report comes amid deepening concerns in Beijing over a fledgling independence movement in the city. The High Court this week backed a government demand to bar two recently elected lawmakers, who insulted China when taking their oath of office, from the legislature.

In a statement after the report’s release, the Hong Kong government said the “one country, two systems” principle was being implemented successfully, as was the city’s role as a global commercial hub. It also urged foreign parties not to interfere.

The booksellers were involved in the production and sale of gossipy political titles banned in mainland China but freely available in Hong Kong. Their plight fuelled Western governments’ concerns and sparked formal diplomatic protests.

One of the five men, Swedish passport holder Gui Minhai, who disappeared from the Thai resort of Pattaya last October, is the only one still in detention in China.

Another, Lam Wing-kee, returned to Hong Kong in June, saying he had been held captive by Chinese agents for eight months.

The report places the worsening climate in the city in the context of China’s broader disregard for international legal agreements and norms on issues such as the South China Sea and Taiwan.