A brief and rare deployment of Chinese troops in Hong Kong to clean up streets has raised questions about whether Beijing will intervene militarily to end nearly six months of pro-democracy protests.
While some residents lauded the troops for helping to clear streets from debris left by protesters, others in Hong Kong read the hour-long action as a warning from Beijing.
Here are key questions and answers on the issue:
Following one of the most violent and intense weeks in the crisis, dozens of soldiers in sports gear rather than military fatigues emerged on Saturday from the Chinese People's Liberation Army's barracks in an upper-class district of Hong Kong.
The men picked up bricks and other objects left on the street outside their barracks by protesters, who throughout the previous week had choked traffic city-wide with debris.
They also jogged in formation up and down one road, with the operation filmed by local media and bystanders.
The PLA later confirmed that it had acted to open the road outside their Kowloon Tong barracks to traffic.
Since its handover from the British in 1997, Hong Kong has been governed under a "one China, two systems" model that allows the territory a degree of autonomy.
As part of this autonomy, Hong Kong's Basic Law states the city government shall be responsible for maintenance of public order.
The PLA is allowed to maintain a garrison in Hong Kong and although the law states troops stationed in the city "shall not interfere in the local affairs of the region", there are important caveats.
Article 14 of the Basic Law states the city government authorities may ask, "when necessary," the central government for assistance from the garrison "in the maintenance of public order and in disaster relief."
Article 18 also allows the central government to effectively suspend Hong Kong's laws if there is a "state of war" or "turmoil" which "endangers national security or unity".
A spokesman for the Hong Kong government said on Saturday that the city had not requested the troops' assistance, and that the clean-up was "initiated by themselves".
It was an "unmistakable" reminder that deploying the PLA remains an option for China's central government, according to Willy Lam, a Hong Kong-based political analyst.
"(The troops) presented a very amicable, peaceful persona to the Hong Kong public," Lam said of the clean-up.
"However, the other side of the message was that they could at any moment's notice participate in the much tougher job of suppressing the so-called rioters."
Chinese defence ministry spokesman Wu Qian on Monday referred to Xi's comments when he defended the clean-up operation, as he repeated warnings about military force.
"(The garrison) has the determination, confidence and capabilities to safeguard sovereignty security and development interests of Hong Kong," Wu said, referring to the Basic Law.
Beijing remains unlikely to mobilise the PLA to suppress demonstrations while other options remain, Lam told AFP, with the military intervention a last resort because of the political sensitivities.
If Beijing was to deploy security forces, it would more likely use the paramilitary People's Armed Police or law enforcement officers from the neighbouring mainland province of Guangdong.
"The PAP are not part of the Hong Kong garrison, so politically it is less sensitive than using soldiers on the streets of Hong Kong," Lam said.
Lam said it would be "difficult" to know when or if the PAP are deployed.
"This would be done surreptitiously they would be wearing the uniform of the Hong Kong police."