The Turkish and Russian presidents on Tuesday discussed an upcoming three-nation leaders’ summit on Syria over the phone, Turkish presidential sources said.

Recep Tayyip Erdogan and his Russian counterpart Vladimir Putin also discussed bilateral relations, said the sources, who asked not to be named due to restrictions on talking to the media.

They also affirmed the determination to further develop bilateral ties, according to the sources.

The summit in the Turkish capital Ankara on April 4 will be attended by the Turkish, Russian, and Iranian leaders discussing the ongoing situation in Syria as the three countries which brokered the Astana peace process on Syria.

During the phone call, Erdogan offered condolences to Putin over a fire at a shopping mall in Siberia that killed at least 64 people, including 41 children.

The fire in the city of Kemerovo started on the mall’s fourth and top floors on Sunday and then consumed an area of about 1,600 square meters.

Three days of mourning in Kemerovo started on Tuesday.