Most of the Russian trucks that "unlawfully" entered Ukraine on Friday had exited the country by Saturday, Ukraine's president told Vice President Biden in a phone call Saturday.
Biden applauded Ukraine and President Petro Poroshenko's "restraint in the face of Russia's blatant provocation and disregard for Ukraine's sovereignty," according to a White House readout of the call.
Biden said the United States and other Group of Seven leaders, which Russia was suspended from earlier this year, would continue to respond to "Russia's destabilizing actions."
Russian trucks, supposed to be carrying humanitarian aid to civilians in the rebel-controlled city of Luhansk, crossed the border Friday without a Red Cross escort or permission from the Kiev government, violating a tentative agreement worked out between the two countries.
Separately, the State Department expressed shock Saturday at reports that Lithuania's honorary consul, Mykola Zelenec, was abducted and murdered by separatists in the rebel-controlled city.
"While we are still seeking information on the circumstances of this tragedy, one thing is clear: For too long people of courage in Ukraine have risked abduction, torture, and even death for their commitment to transparency in the face of cynical armed attempts to dictate Ukraine’s future," State Department spokeswoman Marie Harf said.
The United States and the European Union have imposed a number of rounds of sanctions against Russia after its annexation of Crimea earlier this year and charges that it has continued to support pro-Russian rebels in the country.
Obama spoke with German Chancellor Angela Merkel ahead of her trip to Ukraine a day earlier.
Obama and Merkel reiterated their call for Russia to stop the flow of military personnel and equipment into Ukraine, and called for a bilateral ceasefire.
Merkel was scheduled to meet with Poroshenko on Saturday during her visit, a day ahead of Ukraine's Independence Day.