Delegates at a meeting of countries signed up to the International Criminal Court neared a deal on Monday on allowing the tribunal to prosecute crimes involving countries that invade or attack another.
The compromise at the Kampala review conference of the ICC on crimes of aggression, as they are called, centres on the United Nations Security Council's role in determining whether an act of aggression took place.
Delegates also spent time agreeing on a definition of the crime of aggression, one of four grave crimes over which the ICC has jurisdiction, but one it is yet to tackle due to political sensitivities.
A draft paper circulated by Argentina, Brazil and Switzerland giving primary, but not an exclusive, role to the Security Council in determining whether an act of aggression took place was largely welcomed by delegates as "a way out".
"I think we're cautiously optimistic we're going to have a result. One cannot predict this absolutely, because things can develop quickly at a certain junction," said Jordan's Prince Zeid, who chaired a working group on the crime of aggression.
The draft paper also gives a role to the ICC prosecutor and pre-trial judges in determining whether an investigation should be launched, eliminating earlier options of giving power to the International Court of Justice or the UN General Assembly.
But Richard Dicker at Human Rights Watch raised concerns the proposal would grant the ICC those powers only after seven eighths of member states ratified or accepted the agreement, while keeping jurisdictional powers with an 'external filter'.
"These efforts, if successful, would give the Security Council effective control over the crime of aggression for the indefinite and long-term future," Dicker said.
The crime of aggression is broadly defined as the use of force that manifestly breaches the UN charter and includes an invasion, a bombardment, port blockade or a country allowing a state to use its territory to attack a third nation.
Legal experts say what is at stake in an extended ICC mandate is the impact on the use of force, such as NATO's bombing of Kosovo in the 1990s or more recently Colombia's raids in Ecuador against FARC rebels.
While Security Council members have urged that a probe should follow a Council determination that an act of aggression took place, NGOs and other delegates have said this could undermine the independence of the ICC.
The United States withdrew its support for the ICC in 2002 under then president George W. Bush, worried its troops could face politically motivated prosecutions over unpopular wars but has more recently started to re-engage with the court.