"We have identified witnesses in 17 countries. Well over 100 potential witnesses have been screened, and a number of formal statements have already been taken," he said.
Given the prevailing climate of insecurity and the current absence of an effective system of protection for victims and witnesses, however, all investigative activities had so far taken place outside Darfur.
The prosecutor noted that the next phase of the investigation would focus on a selected number of criminal incidents and those persons bearing greatest responsibility.
"I would like to emphasise that no decisions have been taken at this stage as to whom to prosecute," he added.
During a visit to the Sudanese capital of Khartoum from 17-24 November, the ICC made a request to the Sudanese authorities to undertake several interviews that could provide insight into the activities of all parties to the conflict in Darfur.
Sudanese Minister of Justice Mohammed Ali al-Mardi, however, said that the ICC investigation requested by the Security Council was unnecessary because the Sudanese judicial system was capable of prosecuting any crimes in Darfur.
"The ICC officials have no jurisdiction inside the Sudan or with regards to Sudanese citizens," Mardi was quoted by Reuters news agency as saying. "They cannot investigate anything on Darfur - they have no jurisdiction. This is quite clear and they know it."
As Sudan was not a party to the treaty establishing the ICC, a referral from the Security Council, under resolution 1593 on 31 March, was the only way for the court to have jurisdiction over the Darfur cases.
"The investigation of the situation in Darfur is taking place within a context of ongoing violence and multiple efforts to secure peace, as well as a complex process of political transition," Ocampo said.
Although the ICC would continue to be sensitive to these dynamics, he emphasised that "accountability for the most serious crimes alleged to have been committed in Darfur are an essential component to effective peace and effective transition."
In a report released on Sunday, the New York-based advocacy organisation Human Rights Watch claimed that Sudanese President Umar al-Bashir and other senior officials should be investigated for crimes against humanity in Darfur and placed on a UN sanctions list.
The looting and destruction of villages was not just condoned by government officials, the report noted, it was also methodically organised, with troops and militia members permitted to take land, livestock and other civilian property after killing, raping and torturing tens of thousands of people.
The Darfur conflict erupted in February 2003 when rebels took up arms to fight "discrimination and oppression" by the Sudanese government. According to the UN, the conflict continues to affect some 3.4 million people, of whom 1.8 million are internally displaced and 200,000 have fled to neighbouring Chad.