German Chancellor Angela Merkel arrived in Ukraine on Saturday where she is scheduled to meet with President Petro Poroshenko.
Her visit comes a day after she spoke with President Obama by phone in which both leaders agreed that Russia committed further "provocation and a violation" of Ukraine's sovereignty by moving aid trucks into Ukraine without permission.
However, an Organization for Security and Cooperation in Europe observer told Agence France-Presse there could be no confirmation on how many trucks remained in the country.
"We very much condemn the flagrant violation of Ukraine's sovereignty that we saw today with the movement of this Russian convoy," deputy national security adviser Ben Rhodes said a day earlier.
The first few dozen 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.
While in Ukraine, Merkel announced a more than $650 million aid package for Keiv, according to the BBC, to help with infrastructure and to aid refugees.
Merkel's trip comes days before Poroshenko meets with Russian President Vladimir Putin on Tuesday.
During the call with Obama on Friday, the leaders both expressed concern over Russian troops massed at the border, Russian military in Ukraine, and the shelling of Ukraine territory coming form Russia.
They reiterated their call for Russia to stop the flow of military personnel and equipment into Ukraine, and called for a bilateral ceasefire.
The United States and the European Union have already imposed numerous rounds of sanctions on Russian officials and business related to its action in Ukraine.