A Turkish policeman opened fire on Karlov while he was delivering a speech at the opening of a photography exhibition, in an assassination that stunned Russia and Turkey.
An Ankara court agreed to a request by prosecutors for a ban on broadcasting images of the assassination -- which was caught on film -- as well as the investigation itself, the state-run Anadolu news agency said.
This includes news concerning witnesses, victims or suspects in the murder.
The ruling said such news could be prejudicial to the investigation and to national security. The ban will last for the duration of the investigation.
It was not clear what had prompted the ban one week after the December 19 murder but it came one day after the daily Hurriyet published a detailed interview with the sister of the murderer Mevlut Mert Altintas.
The sister, named as Seher O., said her brother had been "brainwashed" while attending police school in Izmir, AFP reported.
Turkish President Recep Tayyip Erdogan has said Altintas was a member of the group of US-based preacher Fethullah Gulen blamed for the July 15 coup.
However this has yet to be echoed by Russian officials, who say it is too early to comment on the investigation.
In recent years, Turkish authorities have repeatedly placed broadcast bans on sensitive issues and in the wake of attacks, citing national security.
Critics say freedom of expression has declined in Turkey after Erdogan became president in August 2014 but the government has insisted everything is done within the framework of the law.