Combined diplomatic and humanitarian efforts aimed at bringing peace to Syria looked to move to the next level Sunday after the United Nations envoy to the war-torn country confirmed that he would host talks between Syrian opposition and President Bashar Assad's government officials.

Staffan de Mistura told reporters after preliminary talks in Geneva that he was “optimistic and determined” after convincing officials from both the Syrian opposition and Assad's regime to change their minds about taking part in combined talks.

“It is an historic occasion not to be missed,” Mistura said, as he left a Geneva hotel after meeting with the opposition. U.N. officials said the encounter was informal but hoped that a more formal meeting could take place later in the day, according to a Voice of America report.

U.S. Secretary of State John Kerry called on both sides to take part in the talks, but he also said that Assad must allow aid to reach starving citizens stranded in cities and towns across the country, according to a State Department statement.

“The goal is to reduce the violence, isolate terrorist groups such as Daesh [the arabic acronym for the Islamic State group], and create the basis for an inclusive, peaceful and pluralistic Syria we all seek,” said Kerry. “The world is hoping that both sides will move quickly to meet the needs of millions of desperate Syrians, to reduce the pressure on neighboring countries, to reduce the levels of migration and to help restore peace and stability.”

Kerry also said that the main topics on the agenda for negotiations would include a nationwide ceasefire and establishing a path to a political transition that would end the war in accordance with the Geneva Communique of 2012 and U.N. Security Council Resolution 2254.