WASHINGTON -- US Secretary of State John Kerry on Monday urged Russia to "take concrete steps" to help implement the agreement aimed at defusing tensions in Ukraine.

In his telephone talk with Russian Foreign Minister Sergei Lavrov, Kerry urged Russia to publicly call on "separatists to vacate illegal buildings and checkpoints, accept amnesty, and address their grievances politically," State Department spokeswoman Jen Psaki said at a press briefing.

Russia, Ukraine, the European Union and the United States signed an agreement in Geneva last Thursday to de-escalate crisis in Ukraine, but militants in eastern Ukraine refused to heed the deal.

Kerry told Lavrov that Russia needs to demonstrate commitment to the Geneva agreement "in both its rhetoric and its actions" and "what is needed is true de-escalation," Psaki said.

The top US diplomat also called on Russia to assign a senior diplomat to work with the mission of Organization for Security and Cooperation in Europe in eastern Ukraine to "make absolutely clear to the separatists that Russia supports the agreement and wants de- escalation."

On Monday, the White House reiterated that Russia could face additional sanctions if it fails to help ease the tension in Ukraine.

"If there is not progress within days, we remain prepared, along with our European and G-7 partners, to impose additional costs on Russia for its destabilizing actions," White House spokesman Jay Carney told a press briefing.

On Monday, Lavrov urged the United States to stop threatening Russia with sanctions while turning a blind eye to "atrocities" carried out by Ukrainian militants.