Ban has given himself just days to decide on recommendations made by a panel of experts which handed its report on alleged war crimes to the UN leader on Tuesday.
The United Nations said the report will be published and, according to diplomats, major behind-the-scenes lobbying has begun over what steps might then be taken.
According to UN estimates, at least 7,000 civilians died in the final push by government troops against the separatist Liberation Tigers of Tamil Eelam (LTTE) who were defeated in May 2009.
Human Rights Watch has estimated that tens of thousands were killed or injured and Amnesty International put the toll at more than 10,000.
Sri Lanka denied any war crimes took place, rejected the formation of the expert panel as interference in its internal affairs and refused to let the three members -- led by former Indonesian attorney general Marzuki Darusman -- into the country.
UN deputy spokesman Farhan Haq said Ban would study the report and "will determine hi