Rancho Mirage, California CNN  — 

President Barack Obama urged Russian President Vladimir Putin to end his air campaign against Syrian opposition forces during a phone call Saturday, the White House said, a day after Putin’s deputy described relations between Moscow and Washington sinking to Cold War depths.

In a description of the phone call, the White House said Obama stressed “the importance of rapidly implementing humanitarian access to besieged areas of Syria and initiating a nationwide cessation of hostilities.”

ISIS brings Putin, Obama together

Russia entered the Syria conflict in September, launching air strikes on forces aligned against Syrian President Bashar al-Assad from an airbase in Latakia province. U.S. officials have decried the strategy, saying Putin is desperate to keep Assad in power since Russia’s sole remaining military base in the Middle East lies near Syria’s Mediterranean coast.

The U.S. says Russia’s air campaign has killed scores of civilians and jeopardizes the prospects of a peace accord in the civil war-wracked nation.

“President Obama emphasized the importance now of Russia playing a constructive role by ceasing its air campaign against moderate opposition forces in Syria,” the White House said after Obama’s phone call with Putin Sunday.

The Syria situation has driven relations between the U.S. and Russia to new lows. Ties had already been strained by Putin’s intervention in Ukraine and his persistent support for Assad.

Obama’s and Putin’s differences are sharp and dangerous

Russian Prime Minister Dmitry Medvedev called the iced-over relationship “a new Cold War” in comments Saturday.

Speaking at the Munich Security Conference in Germany, Medvedev cited recent NATO moves to bolster its presence in Eastern Europe as a counter to Russian aggression.

“NATO’s policy with regard to Russia has remained unfriendly and opaque. One could go as far as to say that we have slid back to a new Cold War,” Medvedev said. “Almost on an everyday basis we are called one of the most terrible threats either to NATO as a whole or to Europe, or to the United States.”

Obama and Putin discussed Ukraine in their phone call Saturday, both the White House and the Kremlin said.

“The President also urged combined Russian-separatist forces to fulfill their Minsk obligations, especially adhering to the cease-fire,” the White House said, referring to the long-ignored Minsk peace accord that was agreed to a year ago.