The United States was delighted that Putin had asked the upper chamber of Russia's parliament to retract a law enabling him to intervene militarily in Ukraine, Kerry said, "but it could be reversed in 10 minutes," Reuters reports.
Putin should prove his commitment to peace in Ukraine, Kerry told a news conference after NATO foreign ministers met.
"Until Russia fully makes that kind of commitment to the peace process and to the stability of Ukraine, the United States and Europe are compelled to continue to prepare greater costs, including tough economic sanctions, with the hopes that they will not have to be used."
"But that is dependent on the choices that Russia and its President make in the next days and weeks," he said.
EU leaders are due to meet in Brussels on Friday and could consider more economic sanctions against Russia if it fails to support Ukrainian President Petro Poroshenko's peace plan.
A senior Obama administration official said last Friday that the United States had stepped up talks with the European Union about imposing additional sectoral sanctions on Russia because of the flows of Russian military equipment to Ukraine.
The official, speaking on condition of anonymity, said the sanctions would be targeted primarily at the financial, defense and high technology sectors.
Kerry said the United States and its allies were preparing sanctions in case the peace effort in Ukraine failed.
"We believe it is critical for President Putin ... to stop the flow of weapons and fighters across the border, to call publicly for the separatists to lay down their arms, to pull Russian forces and equipment back and to help get OSCE hostages released," he said, referring to Organisation for Security and Cooperation in Europe monitors held in Ukraine.