Ukraine has already given the global court the authority to investigate crimes on its territory from Nov. 21, 2013, to Feb. 22, 2014, the period leading up to the fall of Ukraine's former president Viktor Yanukovich, a Moscow ally.
Russia annexed Crimea soon after, and later in 2014 fighting erupted in eastern Ukraine between Kiev's forces and pro-Russian separatists.
Kiev accuses Russia of driving the rebellion with its arms and troops, which Moscow denies.
The investigation so far excludes any crimes that might have been committed by Russian-backed troops.
A wider probe, including the annexation of Crimea to the present, could for the first time consider allegations of direct Russian involvement.
"We are quite optimistic about more, definitely more, engagement of the ICC," Pavlo Klimkin told Reuters before meeting the court's president and prosecutor on Friday.
An ICC referral would cover "everything under the (ICC) mandate, including crimes against humanity", he said.
Despite the meeting with ICC officials, it was not immediately clear whether Ukraine had made an official referral.
If and when the referral is made, it would have to be considered by the court, which would decide whether to open a preliminary examination that could result in a full investigation - usually a lengthy process.
ICC prosecutors did not immediately respond to requests for comment.
Klimkin highlighted an attack on the port of Mariupol in eastern Ukraine which killed 30 in January as an example of what Ukraine saw as a crime against humanity.
"The shelling killed, in seconds, more than 30 people and heavily wounded 100 people," Klimkin said.
"If you deliberately shell and, I stress, deliberately shell cities, killing civilians, it's a completely different situation (from military operations) and we have to engage the ICC."
There was no official Russian reaction to his comments.
But a source at the Russian Foreign Ministry said Kiev itself was harming people living in the rebel-held east Ukraine by curbing money flows and economic ties with the region.
"If they are so worried with crimes against humanity they should better end the blockade of their own citizens," the source said.
What Moscow refers to as Kiev's "economic blockade" of the rebel-held territory has exacerbated a humanitarian crisis there and further complicated the local civilian population's every day struggle to make a living in the conflict zone.
ICC prosecutors began their initial preliminary inquiry last April after Ukraine's government asked them to look into allegations that Yanukovich's troops had killed more than 100 protesters in Kiev and other cities.
Alex Whiting, a former senior ICC prosecutor, said a new referral could force an investigation of the wider conflict.
"Here (Crimea and eastern Ukraine) there have been widespread allegations of war crimes and even crimes against humanity, so it will be much harder to ignore," he said.
Klimkin said an amnesty granted to suspects in the conflict by the Minsk ceasefire agreement would not apply to crimes that fell under the ICC's statute.
Set up in 2002 to try serious crimes where national authorities are unable or unwilling to intervene, the ICC has been criticized for its failure to act in some of the world's most serious conflicts.
Ukraine is also examining the possibility of launching a case against Russia at another court in The Hague, the International Court of Justice, the highest U.N. court for territorial disputes, Klimkin said.
Source: Google News