US President Barack Obama and his Ukrainian counterpart Petro Poroshenko on Friday expressed their "deep concern" about the recent violence in eastern Ukraine and called on Russia to abide by a ceasefire accord reached in February.

Obama spoke with Poroshenko on the phone Friday about the conflict in eastern Ukraine and the upcoming discussions about the Ukraine crisis at the Group of Seven (G7) Summit, the White House said.

The two leaders "once more called on Russia and the separatists it backs to abide strictly by the terms of the February Minsk Implementation Plan," the White House said in a statement.

Ukrainian authorities said Thursday that dozens of people were killed in the east of the country over the past day as fighting flared up in the restive areas, putting additional strain on a four-month-old ceasefire.

In the telephone talk, Obama reaffirmed the strong US support for Ukraine's sovereignty and territorial integrity, and reiterated his determination to continue working with international partners to provide the support Ukraine needs as it undertakes transformational reforms.

Obama also underscored the US commitment to supporting a diplomatic resolution to the conflict in eastern Ukraine and the need to maintain costs on Russia and the rebels until they fulfill all provisions of the Minsk agreements.

Leaders of the G7 industrialized countries, including Canada, France, Germany, Italy, Japan, Britain and the United States, will be meeting at Schloss Elmau in the German state of Bavaria on June 7 and 8. The Ukraine crisis is expected to be high on the agenda at the summit.

Earlier, White House officials had said Obama is going to urge EU leaders at the G7 meeting to continue anti-Russian sanctions imposed over Moscow's alleged intervention in the Ukraine crisis.

Russian Prime Minister Dmitry Medvedev noted Friday that Moscow would decide whether to extend restrictive measures against western countries considering "actions of its partners".

"Judging by their statements, they still do not want or plan to return to the (Russian) market, and we are not going to beg them," Medvedev said.