President Barack Obama and Russian President Vladimir Putin have agreed to keep up negotiations over a cease-fire agreement for Syria. That's according to a senior Obama administration official who spoke on grounds of anonymity because the person wasn't authorized to speak publicly. The official says Obama and Putin met for 90 minutes on Monday at the Group of 20 economic summit in Hangzhou, China. Their discussion came hours after top US and Russian diplomats failed to seal a deal aimed at providing access to humanitarian aid for thousands of civilians in the war-torn country. The plan would forge an unlikely US-Russian militarily partnership against extremist groups operating in Syria. The official says Obama and Putin clarified remaining gaps in the talks, which largely involve how the deal would be implemented. A senior State Department official said a fresh round of talks between Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov on the margins of the G20 summit in Hangzhou had ended without agreement. The civil war has killed more than 250,000 people and displaced 11 million, causing a refugee crisis in the Middle East and Europe, and contributing to a rise in militant extremist groups. There had been hopes of a breakthrough in stemming the Syria conflict after the US said it was close to a deal with Russia. But frantic diplomacy ended in failure, with Moscow accused of backtracking. A US official said "differences remain" despite two rounds of talks between Secretary of State John Kerry and his counterpart Sergei Lavrov on the sidelines of the summit. — Agencies