The military said any event was banned because the Liberation Tigers of Tamil Eelam (LTTE) was still a proscribed organisation, four years after the army defeated the group to end a decades-long separatist war.
Small and low-key ceremonies are usually held at this time every year to commemorate rebels killed during the conflict, a so-called "heroes' week" that coincides with the anniversary of the death of the first rebel.
Local media have reported that more organised events were planned this year in the island's former northern war zone after the main Tamil party won local elections there in September.
"Promoting and propagating separatist ideology within Sri Lanka directly or indirectly, even by using media freedom, and attempting to commemorate or glorify terrorists that belonged to a proscribed organisation would be illegal," the military spokesman said in a statement.
The week also coincides with the anniversary of the birth of LTTE supremo Velupillai Prabhakaran, who was kil