( CNN ) -- U.S. Secretary of State John Kerry warned his Russian counterpart , Sergey Lavrov , on Saturday that `` Russia should not intervene in Ukraine under the guise of humanitarian convoys or any other pretext of 'peacekeeping , ' '' according to a senior State Department official . Kerry urged `` all parties to work through international organizations '' to provide humanitarian assistance in eastern Ukraine , the official said . In a separate call Saturday , U.S. Vice President Joe Biden and Ukrainian President Petro Poroshenko agreed that any Russian action in Ukraine , even for purported `` humanitarian '' purposes , without the formal , express consent and authorization of the Ukraine government would be `` unacceptable and a violation of international law , '' according to the White House . Russia has denied allegations that it is supporting separatists in Ukraine and maintains it wants to see a diplomatic solution to the ongoing crisis there . But U.S. and Ukrainian officials have accused Russia of saying one thing while doing another : increasing troop levels along the border and continuing to send support to pro-Russian separatists . Pro-Russian separatists say 'fight to the death ' Despite claims by Ukrainian officials , the pro-Russian separtists hold firm that Ukrainian forces `` have never been able to take over the Donetsk districts '' -- the hotbed of violence in eastern Ukraine . The self-proclaimed leader of the Donetsk people 's republic said on Saturday that pro-Russian separatists would consider a humanitarian cease-fire to bring aid to civilians but they are not ready to surrender their territory and would `` fight to the death . '' `` We are ready for ceasefire to avoid escalation of the humanitarian disaster in Donbass , '' Alexander Zakharchenko , prime minister of the self-styled Donetsk People 's Republic in a statement , said , referring to the populous region that includes Donetsk . Earlie this month , The United States and European Union increased economic sanctions on Moscow for supporting pro-Russian separatists fighting Ukraine government forces in the eastern regions of Donetsk and Luhansk , along the border with Russia . Ukraine : Rebel leader resigns ; militants shoot down fighter plane . What is Putin 's endgame in Ukraine ? Who are Ukraine 's pro-Russia rebels ?
Kerry and Bush take measures to ` ` ' an ' humanitarian catastrophe '' Pro - Russian government to consider humanitarian cease - fire . The ongoing conflict has killed close to 100 people -- civilians and combatants .