UN chief Ban Ki-moon called Monday for greater global support for war crimes prosecutions at the International Criminal Court, saying that it acted as a deterrant against atrocities in times of conflict.
Ban was speaking at a conference to review the work of the Hague-based tribunal, created under the 1998 Rome Statute that entered into force four years later.
The court has since spearheaded efforts to punish genocide, crimes against humanity and war crimes, issuing the world's first war crimes warrant for a sitting leader, Sudan's President Omar al-Beshir, over atrocities in Darfur.
The tribunal has also faced obstacles, including a lack of cooperation in arresting suspects and the refusal of the United States to join the court.
More than 100 countries have nevertheless signed on to the court, whose creation was urged by small states seeking ways to prosecute the worst war crimes when their own legal systems were unable to do so.
"We want to send a strong message that atrocities and heinous crimes cannot go unpunished," the UN secretary general said. "We want to bolster the court's deterrent effect and make potential perpetrators think twice before they act."
The court "must have universal support," he said. "Otherwise we simply embolden those who would commit terrible crimes and those who might want to see the court fail."
The United States, Russia and China are the court's biggest hold-outs, but Washington has in recent years cooperated with its investigations, particularly over Darfur.
"The United States has been cooperating wherever they could," Ban said. "Under the leadership of President (Barack) Obama, there is a new engagement policy."
Ban and senior ICC officials also sought to assuage concerns that Africa is being singled out, since all five cases currently under investigation are on the continent.
One of the most contentious issues at the conference is an extension of the court's jurisdiction to the crime of aggression, essentially criminalising the starting of a war of aggression.
The head of the court's management body Christian Wenaweser said he was "cautiously optimistic" member states could strike a deal on aggression.
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 and decide whether a war is just.
One diplomat who took part in the 1998 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.
The court's prosecutor Luis Moreno-Ocampo argues that the ICC's existence is changing the way leaders and armed forces across the world behave, but says nations need to provide more support, especially on enforcing arrest warrants.
"Massive crimes require a careful plan. Certainty that these crimes will be investigated and prosecuted will modify the calculus of the criminals, will deter the criminals, will protect the victim," he told the conference.
With investigations under way in the Democratic Republic of Congo, Sudan, the Central African Republic, Uganda and Kenya, 13 arrest warrrants have been issued but only four suspects are in ICC custody.