Kerry also said he looked forward to a “frank conversation” with French Foreign Minister Jean-Marc Ayrault on “what potential next steps are” to deal with the siege of Aleppo, where more than 250,000 civilians may be trapped.
The United Nations formally declared Aleppo under siege earlier this week.
“We intend to jointly figure out how best to be able to deliver the strongest message possible about the actions that might be taken to deal with this bombing of Aleppo, the siege in — in the 21st century, this entire siege of innocent people,” Kerry said.
The call for a war crimes investigation comes after Kerry officially suspended negotiations with Russia over implementing a cease-fire in Syria on Monday.
Since the end of the temporary cease-fire last month, the Syrian regime, assisted by allied Russian air forces, have pounded the rebel-held parts of Aleppo in some of the worst bombing since the war began in 2011.
The administration is currently searching for new options on how to address the five-year civil war in Syria that’s killed more than 400,000.
Kerry also threatened that the U.S. would renew sanctions on Russia if it did not implement the Minsk Protocol with Russia in the next months or arrive at a plan on how it would be implemented.
Kerry said it was “not our desire, but becomes the only thing left to do if we are not able to move forward.”
The Minsk Protocol is a roadmap for resolving the conflict in Ukraine, after Russian forces invaded in 2014 and annexed the peninsula of Crimea.
— Updated at 11:56 a.m.