US President Barack Obama and Italian Prime Minister Matteo Renzi, in a phone conversation, stressed the need for Russia to use its influence over separatists in Ukraine's east to persuade them to "abide by the ceasefire" and for Russia to take "immediate concrete steps" to stop the flow of weapons and militants across the border, Xinhua quoted the White House as saying in a statement.
Insurgents in Ukraine's Luhansk and Donetsk regions Monday agreed to reciprocate to a week-long ceasefire declared by Ukrainian President Petro Poroshenko June 20, which will end June 27.
During their conversation, Obama and Renzi also agreed on the importance of the Ukrainian government and the militants on continuing discussions to implement the peace plan put forward by Poroshenko, the White House said.
It also said they agreed "to coordinate measures to impose additional costs on Russia if it fails to take rapid action to de-escalate the situation in eastern Ukraine".
The peace plan, mapped out by Poroshenko on June 7 in his inauguration speech, calls for a ceasefire, amnesty for militants to lay down their arms, safe conduct for Russian fighters back to Russia, and broad decentralisation of authority to Ukraine's eastern regions.
The upper house of Russia's parliament voted on Wednesday to revoke a resolution approving military intervention in Ukraine at the request of President Vladimir Putin, a move hailed by Washington and Ukraine.
Upper House Chairwoman Valentina Matviyenko said Wednesday that Russia was doing everything possible to assist the peaceful process and de-escalation of the situation in Ukraine, stressing that "Kiev should follow pragmatic approach and common sense for the development of cooperation between the two countries".