Gregory Korte

USA TODAY

WASHINGTON — President Obama called Russian President Vladimir Putin Monday morning for what the White House said was an "intense" conversation about the breakdown of the cease-fire in Syria.

White House Press Secretary Josh Earnest said the purpose of the call was to "make the case to President Putin that he should use his influence with the Assad regime to live up to the commitments that they've made in the context of the cessation of hostilities."

The call came as fighting escalated along Syria's border with Turkey, with Syrian government forces and the U.S.-backed opposition renewing their fighting after a seven-week cease fire.

In its account of the presidential phone call, the Kremlin news service said the two leaders agreed on the importance of upholding the cease-fire and giving the peace talks a chance. But Putin also suggested to Obama that the U.S.-supported moderate opposition has close ties to terrorist groups in Syria.

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The Russians also made a point of noting that the phone call was made at Obama's initiative.

Obama and Putin also discussed Ukraine. The White House said Obama "urged President Putin to take steps to end the significant uptick in fighting in eastern Ukraine." But the Kremlin said it's up to the new Ukrainian government to live up to its end of the 2015 Minsk agreements.

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One topic that did not come up: The recent incidents of Russian planes "buzzing" U.S. ships in the Baltic Sea.

"These kinds of incidents, while provocative and concerning, are not particularly unusual," Earnest said. He said the United States had protested the flight tactics through the military attache at the U.S. embassy in Moscow.