WASHINGTON, Feb. 14 (Xinhua) -- U.S. President Barack Obama on Saturday spoke to Ukrainian and German leaders about the conflict in eastern Ukraine, where a cease-fire was reportedly coming into force as agreed under a new peace deal.

In a conversation with President Petro Poroshenko of Ukraine over the phone, Obama expressed "his sympathy for the mounting toll of the conflict in eastern Ukraine and his deep concern about the ongoing violence, particularly in and around Debaltseve," the White House said in a statement.

Some 8,000 Ukrainian troops had reportedly been encircled by independence-seeking insurgents in Debaltseve, as the conflict that broke out in Ukraine's east in April last year has intensified since mid-January.

Under the agreement signed on Thursday in the Belarussian capital of Minsk at the conclusion of a four-way summit of French, German, Russian and Ukrainian leaders, a cease-fire starting on Sunday local time between the Ukrainian forces and rebels shall be followed by the withdrawal of heavy weapons from the front line and constitutional reform to give eastern Ukraine more autonomy.

In their phone talks, Obama and Poroshenko "emphasized the pressing need for all signatories to implement the cease-fire and protocol agreements" reached in Minsk in September last year and reaffirmed under the new deal, the White House said.

It noted that "both leaders stressed the importance of establishing a lasting peace that respects Ukraine's sovereignty and unity."

Violence around Debaltseve and the agreed cease-fire also dominated Obama's separate phone talks with German Chancellor Angela Merkel.

"The president thanked the chancellor for her tireless efforts to bring the conflict in eastern Ukraine to an end in manner that preserves Ukraine's sovereignty and unity," the White House said.

Poroshenko on Saturday reportedly ordered government forces to start a cease-fire from midnight (2200 GMT) in line with the new Minsk peace agreement.