US says Russia should be investigated for war crimes

Kerry also mentioned the possibility of increased sanctions against Russia over Ukraine.

"Russia, and the regime, owe the world more than an explanation about why they keep hitting hospitals and medical facilities and children and women," Kerry said in a joint press announcement with the French foreign minister, Jean-Marc Ayrault.

"These are acts that beg for an appropriate investigation of war crimes and those who commit these would and should be held accountable for these actions."

He described Russian bombing in Aleppo over the past weeks as "a targeted strategy to terrorise civilians and to kill anybody and everybody who is in the way of their military objectives."

Kerry said that he had invited his French counterpart for discussions on the appropriate response to "deliver the strongest message possible" to Russia.

"I think it is important for us to make it clear publicly, that if we cannot reach an agreement over [the] Minsk [agreement], it will be absolutely necessary to roll over to sanctions, which is not our desire, but becomes the only thing left to do if we are not able to move forward," he said.

At the same time, the Russian parliament also ratified a treaty with Syria today, allowing it to keep its armed forces in the country for as long as it wants.