The two leaders were conversing on the sidelines of theGroup of 20 summithere, according to a US National Security Council spokesman. More details about their discussion were expected later Monday, but US officials said before the summit that Syria and Ukraine would likely be on the agenda of an Obama-Putin huddle.

The exchange came after a US official said talks had ended between US Secretary of State John Kerry and his Russian counterpart Sergey Lavrov, who had been working to negotiate a plan that would have boosted military cooperation between the two nations in an effort to better target terrorists and prevent civilian deaths.