Ocampo said that the ICC had the names of "the alleged perpetrators" of the attack on the peacekeepers' camp in Haskanita, a village about 19km south of Darfur, last September.
"We have information about the names of two commanders who were allegedly responsible for this," Ocampo said before attending a ceremony marking the 10th anniversary of the Rome Statute that set up the court.
"We have to prove the case," he said.
"The rebels have to control their people and they have to help the court, to provide intelligence against those who commit the attack in Haskanita and even arrest them."
"The rebels have to control their people and they have to help the court, to provide intelligence against those who commit the attack in Haskanita and even arrest them," Ocampo said.
'Excluding no one'
He also suggested that the court was looking into recent attacks on the joint UN-African Union peacekeeping force in Darfur, including one in north Darfur on July 8 which left seven troops dead and 22 injured.
"I am excluding no one. I will follow my evidence," he said. "Anytime they commit any attack against peacekeepers, it's under my jurisdiction, and I will mitigate that."
Asked by reporters whether the announcement of the al-Bashir investigation had been timed to help publicise the court's anniversary, Moreno-Ocampo said the decision was solely based on when the evidence was ready and the court's schedule.
With the court about to go on a summer recess, he said, "this was the my last week to do it so I did it when I had my evidence ready".
"I kept my independence and I cannot be a political factor," Ocampo said.
The Sudanese government has refused to co-operate with the ICC and has called the accusations against al-Bashir "politically motivated".
"Ocampo's weak performance in today's press conference did not surprise anybody because this is the same very weak argument he used in The Hague some days ago to indict our president, and when he was cornered by journalists, he was unable to deliver convincing arguments," Abdalmahmood Mohammad, Sudan's UN Ambassador, said on Thursday.
ICC judges are expected to make a decision on whether to issue a warrant for Bashir's arrest in October or November.
Abdalhaleem gave no details about how Khartoum might react if the warrant was issued, but said it would be "a recipe for disaster".
It is a collective responsibility of the council to move together to halt it. Otherwise it is an invitation for a gate of fire on the country," he said.
Fighting erupted in Darfur in 2003 when ethnic African rebels took up arms against the Arab-dominated central government, accusing it of discrimination.
The United Nations has said that 300,000 people have died in the region and more than 2.2 million been displaced, while Khartoum puts the death toll at 10,000 people.