Washington, Feb 11 (IANS/EFE): US President Barack Obama telephoned his Russian counterpart, Vladimir Putin, to discuss the "escalating violence in eastern Ukraine" and Moscow's "ongoing support" for the pro-Russian separatists there.

"President Obama underscored the rising human toll of the fighting and underscored the importance of President Putin seizing the opportunity presented by the ongoing discussions between Russia, France, Germany, and Ukraine to reach a peaceful resolution," a brief communique issued by the White House said Tuesday.

The US president also repeated to Putin that America continued to support "the sovereignty and territorial integrity of Ukraine."

Consequently, he said that if Russia continued "its aggressive actions in Ukraine, including by sending troops, weapons, and financing to support the separatists, the costs for Russia will rise", a reference to the economic sanctions imposed by the European Union and the US.

The president's call came shortly after Ukraine and the pro-Russian separatists agreed Tuesday to a ceasefire and the withdrawal of heavy armaments during the peace negotiations being held in Minsk, Belarus, with the mediation of Russia and the Organisation for Security and Cooperation in Europe (OSCE).

These conversations are the prelude to the summit meeting of Ukraine, Russia, Germany and France to be held this Wednesday in the Belarus capital, considered of key importance for finding a lasting peace.

Hours before speaking with Putin, the US president had conversed with Ukrainian President Petro Poroshenko, to whom he extended his strong support for the current peace negotiations.