Obama and Putin Meet at G-20 Summit, Agree to Keep Working on Syria Pact

— -- President Obama sat down with Russian President Vladimir Putin on the sidelines of the G-20 summit in China on Monday, in a meeting that covered a laundry list of hot-button issues, from cyber attacks on the U.S. to the civil war in Syria and ongoing hostilities in Ukraine.

Addressing core issues on Syria and Ukraine, the two heads of state had a lengthy exchange of views, a senior administration official told ABC News. The official described the talks during the 90-minute sit-down as constructive.

The pair discussed efforts to reduce violence, provide humanitarian assistance and combat terrorist groups like al Qaeda and the Islamic State in Syria.

Negotiations focused on creating a window of calm to allow humanitarian assistance to reach populations in need.

President Obama described the ongoing bombardment of civilians as both a humanitarian crisis and also a driver of terrorism, emphasizing the need for a cessation of hostilities, the official told ABC News.

Although the summit concluded without a deal, the two leaders discussed ongoing efforts to reach an agreement and noted the progress made in the talks between Secretary of State John Kerry and Russian Foreign Minister Sergey Lavrov.

Kerry and Lavrov sat in on the meeting and are making plans to meet again in coming days under instructions to reach an agreement, according to the official.

The official described the remaining differences between the two sides as technical in nature.

On Ukraine, the senior administration official said that Obama stressed the need for full implementation of the Minsk agreement -- a cease-fire pact originally agreed to in 2014 -- and made clear to Putin that U.S. sanctions against Russia will continue if it is not fully implemented.

The official said the two leaders also had discussions on cyber security but did not provide additional details about the scope of the conversation.

ABC News's Jordyn Phelps contributed to this report.