China rebuffed Morrison's calls for an apology after its foreign ministry spokesman Zhao Lijian posted the picture of an Australian soldier holding a bloodied knife to the throat of an Afghan child on Monday.

The US government called China's use of the digitally manipulated image a "new low" in disinformation.

Morrison took to WeChat on Tuesday to criticise the "false image" while offering praise to Australia's Chinese community.

In his message, Morrison defended Australia's handling of a war crimes investigation into the actions of special forces in Afghanistan and said Australia would deal with "thorny issues" in a transparent manner.

But that message appeared to be blocked by Wednesday evening, with a note appearing from the "Weixin Official Accounts Platform Operation Center" saying the content was unable to be viewed because it violated regulations, including distorting historical events and confusing the public.

Tencent, the parent company of WeChat, did not immediately respond to a request for comment.

Australian special forces allegedly killed 39 unarmed prisoners and civilians in Afghanistan, with senior commandos reportedly forcing junior soldiers to kill defenceless captives in order to "blood" them for combat, a four-year investigation concluded.

Australia said last week that 19 current and former soldiers would be referred for potential criminal prosecution.

China's embassy has said the "rage and roar" from Australian politicians and media over the soldier image was an overreaction.

Australia was seeking to "deflect public attention from the horrible atrocities by certain Australian soldiers," it said.

Other countries including the US, New Zealand and France - and the self-ruled island of Taiwan which China claims as its own - have expressed concern at the Chinese foreign ministry's use of the manipulated image on an official Twitter account.

"The CCP's latest attack on Australia is another example of its unchecked use of disinformation and coercive diplomacy. Its hypocrisy is obvious to all," the US State Department said on Wednesday, referring to the Chinese Communist Party.

Jake Sullivan, tapped as national security adviser in the incoming administration of US president-elect Joe Biden, tweeted support for Australia without reference to China.

"America will stand shoulder to shoulder with our ally Australia and rally fellow democracies to advance our shared security, prosperity, and values," he wrote.

US State Department deputy spokesman Cale Brown said the fabricated image of the soldier was "a new low, even for the Chinese Communist Party".

"As the CCP spreads disinformation, it covers up its horrendous human rights abuses, including the detention of more than a million Muslims in Xinjiang," Brown wrote in a tweet.

France's foreign affairs spokesman said on Tuesday the tweeted image was "especially shocking" and the comments by Zhao "insulting for all countries whose armed forces are currently engaged in Afghanistan".

China's embassy in Paris hit back on Wednesday, saying the soldier image was a caricature by a painter, adding that France has previously loudly defended the right to caricature.

WeChat has 690,000 active daily users in Australia and in September told an Australian government inquiry it would prevent foreign interference in Australian public debate through its platform.

Morrison's message had been read by 57,000 WeChat users by Wednesday.

Zhao's tweet, pinned to the top of his Twitter account, had been "liked" by 60,000 followers after Twitter labelled it as sensitive content but declined an Australian government request to remove the image.

Twitter is blocked in China but has been used by Chinese diplomats.

Australian Associated Press