Washington-U.S. President Obama spoke on Wednesday by phone with President Vladimir Putin of Russia.

President Obama emphasized his concerns over the failure of the Syrian regime to comply with the Cessation of Hostilities in Syria.

He stressed the importance of Russia pressing the Syrian regime for a lasting halt to offensive attacks against civilians and parties to the Cessation, noting the importance of fully recommitting to the original terms of the Cessation.

The Presidents confirmed their commitment to defeating ISIS and the Nusrah Front, al-Qaeda’s affiliate in Syria.

President Obama also stressed the necessity for progress on a genuine political transition to end the conflict in Syria, as well as sustained humanitarian access, and he expressed his support for the efforts of U.N. Special Representative for Syria Staffan de Mistura to make progress on those efforts.

Obama will speak with European leaders about the Syrian refugee crisis, Russia and Ukraine, and the aftermath of Britain’s decision to pull out of the EU during the NATO summit on Friday, the White House said.

Speaking with reporters aboard Air Force One on Thursday, White House spokesman Josh Earnest also said Obama and Russian President Vladimir Putin did not reach any agreement for new cooperation in Syria during a phone call they held on Wednesday.

A Kremlin summary of the call said the two leaders agreed to intensify military coordination in Syria.

A senior Obama administration official said Wednesday the U.S. and Russia aren’t currently “conducting or coordinating military operations with Russia, nor is there an agreement to do so.”

NATO’s approach with respect to Russia is a “balance between strength and dialogue,” said Doug Lute, the U.S. permanent representative to NATO.

“So we’re going to do what we need to do on the strength side of the equation, but we’ll equally be open to dialogue with Russia because we think that balance represents the right and responsible approach,” Lute said.