A row has erupted in Malaysia over a satirical photomontage featuring the country's deputy prime minister.
Mr Najib has denied any links with Ms Shaariibuu's murder
An opposition politician put the image on the internet in connection with a controversial murder trial.
It is based on a witness's statement that he saw a photograph of the female victim with the deputy prime minister.
One minister said if people were allowed to make fun of Malaysia's leaders, they might also be tempted to insult the Prophet Muhammad.
Two elite police bodyguards who had protected Deputy Prime Minister Najib Razak are on trial accused of murdering a young Mongolian woman.
Mr Najib's friend and adviser Abdul Razak Baginda is answering charges that he abetted the murder.
Opposition politicians have used Mr Najib's links to the accused to hint at a possible political scandal.
Altantuya Shaariibuu's body was found in a jungle clearing outside the capital, Kuala Lumpur, last November.
Mr Najib has repeatedly denied meeting her or any involvement in the murder.
The original photograph of the two, if it exists, has never been made public but opposition politician Tian Chua created his own and put it on his website.
It is, he said, in the style and spirit of comedy legends Monty Python.
Senior members of the Malaysian government have demanded action be taken against Mr Chua.
Education Minister Hishammuddin Hussein said that if people are allowed to make fun of Malaysia's leaders they would use the same freedoms to insult the Prophet Muhammad as, he said, is done in the West.
Mr Hishammuddin stressed that he was not trying to put Malaysia's leaders on the same level as the Prophet.
However senior members of the conservative Islamic party, PAS, said that by linking the two, he had in effect done just that.