Kerry said he and Lavrov discussed additional steps that need to be taken, and made clear that it was critical for Russia "to withdraw support from separatists and to assist in removing people from the buildings."
The secretary of state said he raised the "reality" of new potential penalties by the West against specific sectors of the Russian economy.
Even as the military observers, members of an Organization for Security and Cooperation in Europe team, gained their freedom, Kerry and Lavrov talked about the ability of the OSCE to perhaps play a larger role in working to de-escalate the crisis.
The insurgents alleged the team was spying for NATO.
"We will both advance ideas about how to do that without any promises of what those possibilities may produce," Kerry said.
Russia denies it is fomenting the unrest in eastern Ukraine. But it did send its former human rights ombudsman to negotiate for the release of the observers as a representative of Russian President Vladimir Putin.
Kerry also condemned the violence in the Black Sea port of Odessa, where at least 42 people died in skirmishes Friday between Ukrainian government supporters and opponents. Government opponents took refuge in a building that caught fire after protesters threw firebombs inside. At least 36 people died in the fire, according to the emergencies ministry.
"All of this violence is absolutely unacceptable, and Russia, the United States, Ukrainians, Europeans, the OSCE — all of us bear responsibility to do everything in our power to reduce the capacity of militants and extremists who are armed to be carrying out these terrorist and violent activities," Kerry said.
"They must end, and everybody with any influence on any party has an obligation to try to bring an end to this violence."