(Adds context and details of increased reward for culprits)
By James Pomfret and Greg Torode
HONG KONG, Feb 27 (Reuters) - A senior Chinese official on Thursday condemned the daylight stabbing of an influential newspaper editor in Hong Kong in a rare bid by Beijing to address rising public anger over China's perceived interference in the financial hub's affairs.
Police have made no arrests nor established any motive for the stabbing of Kevin Lau, a former chief editor of the Ming Pao newspaper, by two men, that left him fighting for his life.
Suspicions have spread, however, that powerful individuals from mainland China or pro-Beijing allies opposed to the city's push for full democracy may have had a hand in the attack.
Lau's condition stabilised on Thursday and he was able to communicate by writing.
His stabbing could cause a backlash against Beijing.
Hong Kong, a former British colony that reverted to Chinese rule in 1997, enjoys considerable autonomy and broad freedom of speech as a capitalist hub. It has been locked in a battle with Beijing's leaders to push through reforms that could culminate in a direct election for its leader in 2017.
Resentment has surged at attempts by Chinese authorities to tighten their grip on Hong Kong as well as proposals to control which candidates can stand in the 2017 poll.
A senior Chinese official in Hong Kong condemned the attack and urged authorities to crack the case swiftly in a highly unusual show of support for a freedom of speech issue amid concerns Beijing propaganda officials have been more aggressively seeking to control the Hong Kong media's discourse on democracy.
Typically Chinese officials would not feel compelled to comment on an incident of this nature.
"We're closely watching the attack...and strongly condemn the unlawful act of the criminals," said Yang Jian, deputy director of China's representative office in Hong Kong, the Liaison Office.
"We firmly support the Hong Kong government to spare no effort, arrest the culprits and punish them in line with the law," he said in remarks broadcast on local television.
Beijing's Liaison Office has long been criticised by pro-democracy activists and politicians as the strategic base for China's multi-pronged yet low-profile campaign to influence Hong Kong and promote Beijing's interests in the city.
The attack took place days after 6,000 protesters massed outside government headquarters to demand the city's leaders uphold press freedom against perceived intrusions from China.
It also followed Lau's replacement by a Malaysian editor with suspected pro-Beijing leanings. That move sparked a newsroom revolt.
Some insiders at Ming Pao say recent exposes on assets hidden offshore by China's elite - in collaboration with the International Consortium of Investigative Journalists (ICIJ) - could have been a factor in the attack.
Martin Lee, a founder of the city's main opposition Democratic Party, said he could not rule out the possibility that political or criminal elements might have staged the attack, thinking they might "do Beijing a favour".
"I suppose (some) people think in their own hearts this could have been related to Beijing," Lee said by telephone.
"I don't see it unless it is some hot-headed fellow...thinking that what was actually done would be in accordance with the wishes of Beijing."
Lee, together with newspaper publisher Jimmy Lai, was the target of a foiled assassination plot in 2008 as he led Hong Kong's pro-democracy movement into a heated election campaign.
The United States and European Union expressed concern over the assault and diplomats in Hong Kong said it underscored fears that the city's freedoms were being eroded.
"There's been a growing sense that, like the rule of law, they (media freedoms) are vital if Hong Kong is to maintain its role as an international centre," said one Western diplomat who declined to be identified.
"This case has only highlighted those fears. The Hong Kong government should know the importance of cracking this case, wherever it leads."
Journalists were defiant and planned more weekend protests.
Around 100 Ming Pao reporters dressed in black gathered outside the paper's headquarters, holding up copies of Thursday's edition carrying a black masthead. Its owners raised the reward for information on the case from HK$1 million ($130,000) to HK$3 million.
"No matter how great a challenge it is, we Ming Pao staff will not stand back, we will speak out for what is important," said Sin Wan-kei, a spokeswoman for the Ming Pao Staff Concern Group. ($1 = 7.7604 Hong Kong dollars)
Additional reporting by Grace Li,; Editing by Ron Popeski