Russia must prove that it is working to help disarm illegal armed groups in the east of Ukraine, U.S. Secretary of State John Kerry has said.

"We are in full agreement that it is critical for Russia to show in the next hours, literally, that they are moving to help disarm the separatists, to encourage them to disarm, to call on them to lay down their weapons and begin to become part of a legitimate political process," Kerry told reporters in Paris on Thursday after a meeting with French Foreign Minister Laurent Fabius.

He said that the European leaders would discuss new sanctions against Russia and "we all agree that they need to be ready."

"But our preference is not to have to be in a sanctions mode. We would like to see a cooperative effort between the United States, Europe, and Russia and the Ukrainians. And we are going to try to encourage that as much as we can," Kerry said.

Fabius, in turn, noted progress in the situation in Ukraine.

"There is some sort of a de-escalation, but we will be very careful," he said.