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

The two heads of state also discussed Ukraine and cyber security.

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.

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

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.