Eight years after the International Criminal Court became operational, member states are set to review its performance and seek how to bring more suspects to trial.

Founded with the 1998 Rome Statute which entered into force in 2002, the Hague-based tribunal is a key instrument of global justice but has faced many obstacles in the cases undertaken so far.

In a statement issued Thursday, UN Secretary General Ban Ki-moon, who is expected in Kampala on Sunday for next week's review conference said the ICC had already proved itself to be more than a "paper tiger."

But he urged member states to "fully cooperate with the court. That includes backing it publicly, as well as faithfully executing its order."

With investigations under way in the Democratic Republic of Congo, Sudan, the Central African Republic, Uganda and Kenya, 13 arrest warrants have been issued but only four are in ICC custody.

"Unless governments actually make arrests, the ICC cannot deliver justice to victims of mass atrocities," Richard Dicker, Human Rights Watch's international justice director, said in a statement.

Uganda, the conference host, violated Ban's directive when it invited Sudan’s indicted president Omar El-Beshir to Kampala and refused to commit to arresting him if he accepted.

With three Sudanese, three Ugandan and two Congolese indictees still at large, delegates are expected to issue a declaration on how to improve cooperation between the court and the member states' security services.

And since all five active investigations are in African countries, some delegates will try to counter the growing impression that the ICC is resented by many on the continent.

"Some leaders have tried to paint Africa as against the ICC, our voices are testament to the fallacy of such claims," a coalition of 124 African civil society groups said in a statement.

African countries were among those who lobbied the hardest for the ICC's creation during the negotiations that led to the 1998 treaty.

One of the most contentious issues to be discussed at the conference in Kampala will be extension of the court's jurisdiction to the crime of aggression.

President of the ICC’s Assembly of State Parties Christian Wenaweser said he was "cautiously optimistic" member states could strike a deal on aggression, which, if put into force, would join war crimes, crimes against humanity and genocide as actionable offenses.

While member states have informally agreed on how aggression should be defined, the real challenge lies in determining who has the power to initiate an investigation.

Wenaweser explained that states have agreed that the United Nations Security Council should have the first say but rights groups argue the body should not have final authority.

"Human Rights Watch has long opposed control of any crime within the court’s jurisdiction by external bodies because it would undermine the ICC’s judicial independence," the New York-based watchdog said.

The issue is complicated because it tends to pit the court’s most powerful member states against the less powerful majority.

The United States is not an ICC member and its war crimes ambassador Stephen Rapp said last year that the Security Council -- where the US and four other powers have a veto -- should decide whether aggression has occurred.

One diplomat who took part in the Rome negotiations said the inclusion of the crime of aggression in the court's jurisdiction would be significant.

"For example, would the invasion of Iraq have been an aggression? That's why it's so political. UN Security Council members do not want to give up their de facto monopoly on the determination of what is an aggression," he said.

"So (the Kampala review) could be a victory for the small states, depending on how it is framed."