HONG KONG/WASHINGTON (Reuters) - The Chinese military commander responsible for Hong Kong has assured a Pentagon official that Chinese troops will not interfere in the city’s affairs – an apparent signal that they will stay in their barracks amid renewed political upheaval.

Trucks full of white-gloved People’s Liberation Army soldiers rolled into Hong Kong within hours of Britain handing its colony back to Chinese rule in 1997, sparking anxiety and raising lingering questions about their role.

Major General Chen Daoxiang was speaking at the start of a meeting last month with David Helvey, principal deputy assistant secretary of defense for Indo-Pacific Security Affairs, according to people briefed on the discussion.

Helvey met Chen on a courtesy call at in the PLA’s Hong Kong headquarters on June 13 – just meters from where a day earlier police clashed violently with protesters seeking to prevent the passing of a now-suspended bill that would allow people to be extradited to mainland China for trial.

Protests and violence have continued since, including some activists smashing their way into the legislature on July 1, daubing the debating chamber in graffiti.

“Major-General Chen made it clear from the outset that the PLA would not breach their long-standing principle of non-interference in Hong Kong affairs,” one source briefed on the discussions told Reuters.

“It was surprising, because he took it upon himself to raise it. It was a clear signal, coming at a sensitive time.”

A U.S. defense official, speaking on condition of anonymity, confirmed that Chen and a senior Pentagon official met.

“Major-General Chen did mention that during a conversation last week,” the U.S. defense official said. “I can’t provide any more context to the conversation in that it was private, between the two leaders.”

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A source with ties to the Chinese military said there were no plans for PLA involvement at the moment.

“This is a Hong Kong matter for the Hong Kong government to resolve,” said the source, who meets regularly with senior officers.

The Chinese Defence Ministry and the PLA Hong Kong garrison did not respond to Reuters’ requests for comment.

The role of the PLA in Hong Kong has long been one of the most sensitive elements of the handover – and a presence closely watched by activists and foreign diplomats.

Some in the city fear the troops could be unleashed to quell violence but police chiefs have insisted their forces are capable of maintaining order.

Hong Kong returned to Chinese rule with a guarantee of its freedoms, including the right to protest and an independent judiciary not enjoyed on the mainland, for at least 50 years. Under its mini-constitution, the Basic Law, defense and foreign affairs are managed by Communist Party leaders in Beijing.

The Basic Law states that Hong Kong can request the garrison’s assistance to maintain public order but “they shall not interfere in local affairs”. They must abide by local laws, which are governed by the independent judiciary.

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VERY HIGH THRESHOLD

Chinese laws allow for the standing committee of China’s parliament, the National People’s Congress, to deploy the garrison if a state of war or emergency is declared for Hong Kong, citing “turmoil” that threatened national security that was “beyond the control of the (Hong Kong) government”.

Legal scholars say that is a very high threshold while some retired security officials say any involvement by PLA units in Hong Kong security would shatter the “one country, two systems” formula under which Hong Kong returned to China.

They would also expect police to secure any PLA facilities targeted by protesters.

Regina Ip, a member of the Hong Kong government’s leading advisory body and a former security chief, said despite “dangerous provocations” from some protesters, there was no appetite among Beijing or Hong Kong leaders for the PLA to become involved.

The bloody crackdown on pro-democracy protesters on June 4, 1989, in and around Beijing’s Tiananmen Square had been a “millstone” on Chinese leaders for three decades and they remained sensitive to international criticism, she said.

“I think the current leadership are smart enough to avoid this,” she said.

A second U.S. official, speaking on condition of anonymity, said the United States noted the Chinese garrison’s low profile.

“If they got to the point where the PLA had to intervene in Hong Kong, it would be a significant admission that they’ve lost control.”

While acknowledging the likely reticence of Beijing deploying the PLA in Hong Kong, security analyst Derek Grossman of the U.S.-based RAND Corporation said there could be no guarantees if protests challenged the core interests of President Xi Jinping and his team.

“The Hong Kong garrison might seem like a symbolic presence, but the bottom line is that you can never really be sure they won’t be used, particularly if things start to move in a whole new direction, such as inspiring protest action on the mainland,” he said.Foreign envoys estimate the strength of the Hong Kong garrison at between 8,000 and 10,000, with troops in bases on both sides of the border. It includes a small naval and air force attachment.

While they stage frequent drills, they are seldom seen outside of their bases.

The PLA still occupies bases formerly used by the British across the territory, including several prime sites on Hong Kong island and across the harbor in Kowloon.

The British-built PLA headquarters, topped by a large neon red and gold star, flanks key government offices and the city’s legislature – a key target of recent protests.