The United States refused to back down Thursday in its support for democracy in Hong Kong after Beijing accused Washington's envoy to the city of meddling in China's internal affairs.

Song Zhe, China's top diplomat in Hong Kong, rebuked Clifford Hart after the newly appointed US consul general said last month when taking office that he looked forward to "progress towards genuine universal suffrage".

Ties between the United States and China are strained after Washington accused Hong Kong's government of acting in bad faith over intelligence leaker Edward Snowden and warned of repercussions.

"Commissioner Song emphasised that the political system development of Hong Kong is its internal affairs. Foreign country governments and officials should not interfere," said a statement Wednesday by Song's office.

Song hoped the US would "refuse to use any excuses to conduct undue activities and refuse to do anything that would hurt Hong Kong's prosperity and stability".

But a spokesman for the US consulate told AFP on Thursday: "The United States' long-standing policy toward Hong Kong is unchanged.

"We support Hong Kong's autonomy under 'one country, two systems' and look forward to Hong Kong's continued progress toward genuine universal suffrage."

Such a transition was in keeping with "the aspirations of the Hong Kong people", the spokesman said.

China has promised the former British colony it will see a transition to universal suffrage by 2017, though critics say little or no progress has been made on the prickly issue as the deadline draws closer.

Hong Kong leader Leung Chun-ying was voted into office in March last year by 1,200 of the city's seven million people, mainly Hong Kong's pro-mainland business elite.

He has seen his ratings plummet with critics accusing him of bowing to Beijing and doing little to address quality-of-life issues.

Sonny Lo, a political analyst, said Song's remarks -- the third such warning to the US in recent months -- were consistent with rising Chinese concerns over foreign influence in its domestic politics.

"Hong Kong's democratic movement has a momentum of its own, independent of US influence," Lo said.

With Hong Kong seeing regular pro-democracy protests, "Beijing seems to be concerned with any possible foreign push that may trigger a larger-scale movement", he added.

Stephen Young, Hart's predecessor, said in June that China was guilty of "misbehaviour" over former NSA contractor Snowden's departure from Hong Kong, despite an extradition treaty.

Hong Kong officials argued that a US request asking for Snowden to be detained was riddled with clerical errors, and there was no legal basis to stop him flying to Russia, where he has been granted asylum.

Hong Kong's semi-autonomous status enshrines civil liberties not seen in mainland China -- including the right to protest -- under the "one country, two systems" handover agreement.